Firstly, "fair use" does not mean you can just take whatever copyrighted material you like and use it.  Non-free content cannot be used in cases where a free content equivalent, with an acceptable quality sufficient to serve the encyclopedic purpose, is available or could be created.  Lifting a definition from an external source, instead of writing your own, is not an example of fair use.
Secondly, as you seem to think that something can only be redundant if it's an exact copy, let's have a look at the two definitions, piece by piece:
 Wikipedia definition Copied definition Comparison A tax (from the Latin taxo; "rate") is a financial charge or other levy According to Black's Law Dictionary, a tax is a "pecuniary burden Equivalent in meaningimposed upon a taxpayer (an individual or legal entity)laid upon individuals or property owners Equivalent in meaningby a state or the functional equivalent of a stateto support the government [...] a payment exacted by legislative authority."  Equivalent in meaningsuch that failure to pay is punishable by law.It "is not a voluntary payment or donation, but an enforced contribution, exacted pursuant to legislative authority"  Equivalent in meaningTaxes are also imposed by many administrative divisions. Taxes consist of direct or indirect taxes and may be paid in money or as its labour equivalent.and is "any contribution imposed by government [...] whether under the name of toll, tribute, tallage, gabel, impost, duty, custom, excise, subsidy, aid, supply, or other name." Oooh!  Slightly different.  And how very useful a list of obscure alternative words for "tax" is too.
If you really, desperately need to include the list of obscure alternative words for "tax", the way to do it is to list some of the terms, and cite the source from which they came.  Simple, huh?  The way not to do it is to copy and paste the entire chunk of text verbatim.
And thirdly, you may be flabbergasted to know that IP addresses are often not static.  The first edit from this IP address is from yesterday.  The first edit from this editor was in 2004.  There is no contradiction there, despite what you seem to want to believe.  201.215.252.50