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Page Number: 8.0

Cite as:  588 U. S. ____ (2019) 

5 

Opinion of the Court 

the  district  court’s  order.    Brief  for  United  States  as 
Amicus  Curiae  35;  accord,  Tr.  of  Oral  Arg.  18–22.  A 
reversal  here  thus  would  ensure  exactly  the  relief  the 
Institute  requests.  That  is  enough  to  satisfy  Article  III. 
Monsanto, 561 U. S., at 152–153. 

III 
A 
As  we’ve  seen,  Exemption  4  shields  from  mandatory
disclosure  “commercial  or  financial  information  obtained 
from  a  person  and  privileged  or  confidential.”    5  U. S. C. 
§552(b)(4).  But FOIA nowhere defines the term “confiden-
tial.”  So,  as  usual,  we  ask  what  that  term’s  “ordinary,
contemporary,  common  meaning”  was  when  Congress 
enacted FOIA in 1966.  Perrin v. United States, 444 U. S. 
37, 42 (1979).  We’ve done the same with other undefined 
terms  in  FOIA.  See,  e.g.,  Milner  v.  Department  of  Navy, 
562 U. S. 562, 569 (2011); United States v. Weber Aircraft 
Corp., 465 U. S. 792, 804 (1984).

The  term  “confidential”  meant  then,  as  it  does  now, 
“private”  or  “secret.”  Webster’s  Seventh  New  Collegiate 
Dictionary 174 (1963).  Contemporary dictionaries suggest 
two  conditions  that  might  be  required  for  information 
communicated to another to be considered confidential.  In 
one  sense,  information  communicated  to  another  remains 
confidential whenever it is customarily kept private, or at 
least  closely  held,  by  the  person  imparting  it.    See,  e.g., 
Webster’s  Third  New  International  Dictionary  476  (1961) 
few”  or  “not  publicly
(“known  only  to  a 
disseminated”);  Black’s  Law  Dictionary  370  (rev.  4th  ed. 
1968)  (“intended  to  be held  in  confidence  or  kept  secret”).
In  another  sense,  information  might  be  considered  confi-
dential only if the party receiving it provides some assur-
ance  that  it  will  remain  secret.  See,  e.g.,  1  Oxford 
Universal  Dictionary  Illustrated  367 
(3d  ed.  1961) 
(“spoken  or  written  in  confidence”);  Webster’s  New  World 

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