The legitimacy of this word rests entirely on two appearances in dictionaries, in 1623 and 1656. It seems never to have been used seriously and ever since has been held up as an example of an odd word, in modern times in works with titles like The Joy of Lex, Poplollies and Bellibones, Have a Word on Me, and Dimboxes, Epopts, and other Quidams.
It means a person whose hair has never been cut. Though that may appear comic to some, there’s nothing humorous in its etymology. The word is from the classical Latin acersecomes, a long-haired youth, a word borrowed from an earlier Greek one that was made up from kome, the hair of the head (which is where comic comes from in the ending), keirein, to cut short, and the prefix a-, not. Though this sounds like an aged curmudgeon’s way to talk about unkempt youngsters who weren’t like that in his day, it was actually neutrally descriptive — it was usual for Roman and Greek youths to wear their hair long until they reached manhood.
Greek kome has given us one sense of coma: a diffuse cloud of gas and dust that surrounds the nucleus of a comet. The same -comic ending turns up in two terms that, if possible, are even rarer: acrocomic, having hair at the tip, as in a goat’s beard (acro- means tip) and xanthocomic, a person with yellow hair (from Greek xanthos, yellow).