Exhibit 4.1


 


SPECIMEN UNIT CERTIFICATE 


 


NUMBER UNITS U- 


	 	 	 	 	 
	
    SEE REVERSE FOR

    CERTAIN

    DEFINITIONS
	 	ONS Acquisition Corp.	 	 


 


CUSIP G67560121


 


UNITS CONSISTING OF ONE CLASS A ORDINARY SHARE
AND ONE-HALF OF ONE 


 


REDEEMABLE WARRANT TO PURCHASE ONE CLASS A ORDINARY
SHARE 


 


THIS CERTIFIES THAT is the owner of Units.


 


Each Unit (“Unit”) consists of one (1) Class A ordinary
share, par value $0.0001 per share (“Ordinary Shares”), of ONS Acquisition Corp., a Cayman Islands exempted company (the “Company”),
and one-half (1/2) of one redeemable warrant (each whole warrant, a “Warrant”). Each Warrant entitles the holder to purchase
one (1) Ordinary Share for $11.50 per share (subject to adjustment). Each Warrant will become exercisable on the later of (i) thirty (30)
days after the Company’s completion of a merger, share exchange, asset acquisition, share purchase, reorganization or other similar
business combination with one or more businesses (each, a “Business Combination”), and (ii) twelve (12) months from the closing
of the Company’s initial public offering, and will expire unless exercised before 5:00 p.m., New York City Time, on the date that
is five (5) years after the date on which the Company completes its initial Business Combination, or earlier upon redemption or liquidation
(the “Expiration Date”). The Ordinary Shares and Warrants comprising the Units represented by this certificate are not transferable
separately prior to , 2021, unless Ladenburg Thalmann & Co. Inc. elects to allow earlier separate trading, subject to the Company’s
filing with the Securities and Exchange Commission of a Current Report on Form 8-K containing an audited balance sheet reflecting the
Company’s receipt of the gross proceeds of the initial public offering and issuing a press release announcing when separate trading
will begin. No fractional warrants will be issued upon separation of the Units and only whole warrants are exerciseable. The terms of
the Warrants are governed by a Warrant Agreement, dated as of [__], 2021, between the Company and Continental Stock Transfer & Trust
Company, as Warrant Agent, and are subject to the terms and provisions contained therein, all of which terms and provisions the holder
of this certificate consents to by acceptance hereof. Copies of the Warrant Agreement are on file at the office of the Warrant Agent at
1 State Street, 30th Floor, New York, New York 10004, and are available to any Warrant holder on written request and without cost.


 


Upon the consummation of the Business Combination, the Units represented
by this certificate will automatically separate into the Class A Ordinary Shares and Warrants comprising such Units.


 


This certificate is not valid unless countersigned by the Transfer
Agent and Registrar of the Company.


 


This certificate shall be governed by and construed in accordance with
the internal laws of the State of New York.


 


Witness the facsimile signatures of its duly authorized officers.


 


	 	 	 	 
	By	                         	 	                        
	 	Chief Executive Officer	 	Chief Financial Officer


 






    


     


    

 


ONS Acquisition Corp. 


 


The Company will furnish without charge to each unitholder who so requests,
a statement of the powers, designations, preferences and relative, participating, optional or other special rights of each class of shares
or series thereof of the Company and the qualifications, limitations or restrictions of such preferences and/or rights.


 


The following abbreviations, when used in the inscription on the face
of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:


 


	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 
	TEN COM	 	—	 	as tenants in common	 	UNIF GIFT

 MIN ACT	 	—	 	 	 	Custodian	 	 
	 	 	 	 	 	 	 	 
	 	 	 	 	 	 	 	 	 	 	(Cust)	 	 	 	(Minor)
	 	 	 	 	 	 
	TEN ENT	 	—	 	as tenants by the entireties	 	 	 	 	 	under Uniform Gifts to Minors Act
	 	 	 	 	 	 
	 	 	 	 	 	 	 	 	 	 	(State)
	 	 	 	 	 	 	 	 
	JT TEN	 	—	 	as joint tenants with right of survivorship and not as tenants in common	 	 	 	 	 	 	 	 	 	 


 


Additional abbreviations may also be used though
not in the above list.


 






    2


     


    

 





	For value received,	 	hereby sells, assigns and transfers unto	 	 






 


PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING
NUMBER OF ASSIGNEE


 


(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING
ZIP CODE, OF ASSIGNEE)


 


Units represented by the within Certificate, and do hereby irrevocably
constitute and appoint Attorney to transfer the said Units on the books of the within named Company with full power of substitution in
the premises.


 


	Dated	 	                       	 	 
	 	 	 	 	
    Notice: The signature to this assignment must correspond
with the name as written upon the face of the certificate in every particular, without alteration or enlargement or any change whatever.

	
    Signature(s) Guaranteed:
	 	 
	THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM, PURSUANT TO S.E.C. RULE 17Ad-15 OR ANY SUCCESSOR RULES).	 	 


 


In each case, as more fully described in the Company’s final
prospectus dated [__], 2021, the holder(s) of this certificate shall be entitled to receive a pro-rata portion of certain funds held in
the trust account established in connection with the Company’s initial public offering only in the event that (i) the Company redeems
the Ordinary Shares sold in its initial public offering and liquidates because it does not consummate an initial business combination
within the period of time set forth in the Company’s amended and restated memorandum and articles of association, as the same may
be amended from time to time, (ii) the Company redeems the Ordinary Shares sold in its initial public offering in connection with a shareholder
vote to amend the Company’s amended and restated memorandum and articles of association (A) that would modify the substance or timing
of the Company’s obligation to provide holders of the Ordinary Shares the right to have their shares redeemed in connection with
the Company’s initial business combination or to redeem 100% of the Ordinary Shares if the Company does not complete its initial
business combination within the time period set forth therein or (B) with respect to any other provision relating to the rights of holders
of the Ordinary Shares, or (iii) if the holder(s) seek(s) to redeem for cash his, her or its respective Ordinary Shares in connection
with a tender offer (or proxy solicitation, solely in the event the Company seeks shareholder approval of the proposed initial business
combination) setting forth the details of a proposed initial business combination. In no other circumstances shall the holder(s) have
any right or interest of any kind in or to the trust account.


 


 


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