1859, thieves' slang, "counterfeit, sham, bad, spurious," a word of unknown origin. Century Dictionary suggests it is a dialectal variant of snithe, itself a dialectal adjective meaning "sharp, cutting," used of the wind, from the Middle English verb snithen "to cut," from Old English snithan, which is cognate with German schneiden.
In earliest use it seems to have been most commonly applied to counterfeit coin. Farmer and Henley ("Slang and Its Analogues," 1903) has it as "bad, wretched, contemptible, or (army) dirty." Of persons, "characterized by low cunning and sharp practice," by 1874 (Hotten). Sense of "sneering" is attested by 1928, perhaps via the earlier noun sense of "hypocrisy, malicious gossip" (1902). Related: Snidely; snideness.
The tradition that a first-rate man is less a first-rate man if, encountering a snide detraction of himself that has no respect for the facts, he makes a critical riposte, strikes me as being just about as silly as anything I have run across during many years spent in this silly world. I speak, of course and obviously enough, not of snide criticism written by essentially snide men, but of the species of snide criticism that is every once in a while written by men who should know better. [George Jean Nathan, "Clinical Notes," The American Mercury, June 1928]
word-forming element meaning "disease," from Greek nosos "disease, sickness, malady," a word of unknown origin.
also key-word, "word which serves as a guide to other words or matters," 1807, from key (n.1) in the figurative sense + word (n.). Originally in reference to codes and ciphers. In reference to information retrieval systems, "word from the text chosen as indicating the contents of a document" (1967).
before vowels bronch-, word-forming element meaning "bronchus," from Latinized form of Greek bronkhos "windpipe," a word of unknown origin.
before vowels log-, word-forming element meaning "speech, word," also "reason," from Greek logos "word, discourse; reason," from PIE root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')."
1680s, from Hebrew gematriya, a transliteration of Greek geometria (see geometry). "[E]xplanation of the sense of a word by substituting for it another word, so that the numerical value of the letters constituting either word is identical" [Klein].