One of the pleasures of getting older is hearing the next generation but two still using quaint out-of-date slang like cool, with it and so on, thus showing themselves to be just as old-fashioned now as they once told us we were.
It is pleasant to find them occasionally using words which they believe to be modern but which we know to be around a hundred years old. Here’s one, its use and origin comprehensively explained in the OED:
Excellent, outstanding; fashionable, ‘cool’.
slang (orig. U.S., esp. in African-American usage).
Forms: 19- def, def', irreg. deaf. [Prob. alteration of DEATH n., originating in the non-standard Jamaican English pronunciation and spelling def, and the use of the word (in both forms) as a general intensifier (see quot. 1907).
Cf. DEATH a.2 The form in quot. 1979 is often interpreted as being a use of DEF a., and is in fact spelt def in many later transcriptions of the song, including that in L. A. Stanley Rap: the Lyrics (1992). However, in the original published lyrics, the word is spelt death, although the pronunciation on the recording itself is indistinct. This song, one of the most celebrated and influential hip-hop records and one of the first to enjoy international commercial success, may in part account for the enduring use of def within the genre and the strength of its association with hip-hop culture.An alternative derivation def' in quot. 1982.]
[1907 W. JEKYLL Jamaican Song; Story lxviii. 171 ‘I never do him one def ting,’ a single thing. ‘Def’ is emphatic, but is not a ‘swear-word’. 1979 G. O'BRIEN et al. Rapper's Delight (song, perf. ‘Sugarhill Gang’), Someone get a fly girl, gonna get some spank and drive off in a death O.J.] 1981 W. SAFIRE in N.Y. Times Mag. 18 Jan. 6/3 Deaf [sic] a mispronunciation of ‘death’ is the current superlative. (In topsyturvytalk, death is the liveliest and baad-baaader-baaadest is the equivalent of good-better-best.) 1982 in S. Hager Hip Hop (1984) 89 A sureshot party presentation... Thurs. January 21... ‘Aanother def' bet’. 1986 Village Voice (N.Y.) 4 Nov. 24/2 ‘It's Yours’ T LA Rock and Jazzy Jay (Partytime, 1984) Here's the first def jam that made the others possible. 1992 Buffalo (N.Y.) News 23 Aug. G1/2 No self-respecting teen-ager in Buffalo who wants to be def listens to the bubble-gum music on classic hits radio. 1996 V. WALTERS Rude Girls xiii. 277 Yeah, that's a def idea. 1999 Y (S. Afr.) June 75/2 Premier's ‘New York State Of Mind Pt II’ is def, the bombest joint.