The AI-powered English dictionary
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(philately) Initialism of extremely fine or extra fine; also EF. examples
(numismatics slang) Initialism of extremely fine.
Initialism of The X-Files. quotations examples
That "Barbie Shippers" faction of XF fandom is currently cloistering itself somewhere in really dreadful, schmoopy fanfic where no other character threatens the purity of their "deep, abiding luv".
2005 June 25, campylobacter, “Re: Never Again question”, in alt.tv.x-files (Usenet)