From the second edition (1989):

acronym

orig. U.S.

(ˈækrənɪm) [f. acr(o- + -onym after homonym.]

A word formed from the initial letters of other words. Hence as v. trans., to convert into an acronym (chiefly pass. and as pa. pple.). Also acroˈnymic a.; acroˈnymically adv.; ˈacronyming vbl. n.; ˈacronymize v. trans.

1943 Amer. N. & Q. Feb. 167/1 Words made up of the initial letters or syllables of other words‥I have seen‥called by the name acronym. 1947 Word Study 6 (title) Acronym Talk, or ‘Tomorrow's English’. 1947 Word Study May 6/2 Some new forms combine the initial syllables (resembling blends) instead of initial letters, as in the case of Amvets (American Veterans' Association)‥but they still are in the spirit of acronyming. Ibid. 7/2 There has definitely been a speed-up in ‘acronyming’. 1950 S. Potter Our Language 163 Acronyms or telescoped names like nabisco from National Biscuit Company. 1954 Britannica Bk. of Yr. 1954 638/1 Typical of acronymic coinages, or words based on initials, were‥mash (Mobile Army Surgical Hospital). 1956 R. Wells in M. Halle et al. For Roman Jakobson 665 Take the WE counterpart of the SE expression to be acronymized (North Atlantic Treaty Organization), and select from each word the first one or two or three letters in such a way that the selected letters, assembled and regarded as one word, will have a normal, pronounceable SE counterpart. 1967 Sci. News 19 Aug. 177/1 The TacSatCom, as it is acronymed, is a small-scale system which should be in the field soon. 1971 Daily Tel. 3 Feb. 12 Has the Establishment realised, inquires an acronymically-minded reader, that if the Industrial Relations Bill becomes law, it will not be only Ireland that is saddled with an IRA? 1972 Sat. Rev. (U.S.) 3 June 30 Nitrogen oxide, acronymed NOx, is another of the plant's noxious by-products. 1981 Amer. Speech LVI. 65 Byte is a fairly far-fetched way of acronymizing binary digit eight. 1981 Maledicta V. 99 Who were the real ‘ethnics’, acronymically speaking? 1983 Verbatim Spring 2/2 Paulies play puck (ice hockey) or hoop (basketball, also acronymed to b-ball).