In the absence of a better answer (that I can find), this would seem to be the most plausible.

Several sources suggest that snog is related to snug, possibly by a back-formation of snogging. Less academic sources ( Punch Magazine, 1929) give definitions such as ' a kind of boy', ' a towel' or ' a kind of bun', none of which seem to help us either. a push with the headĪ vocabulary of the Anglo-Manx dialect - Sophia Morrison, Edmund Goodwin (1924). Snog (Mx.): a nod: The cow gave a snog, ie. (For those that are interested, cock-squoyling is a game that involves throwing sticks (or squoils, snogs) at cocks). Snog, n: a stick used for 'cock-squoyling'Ī glossary of Berkshire words and phrases, Volume 20, Issue 3 - Job Lowsley (1888). The word does seem to have been around for quite a while. Which isn't terribly helpful and is already given in the question. Snog, n: a long kiss or a period of amorous kissing and cuddling: he gave her a proper snog, not just a peck Snog, v (snogs, snogging, snogged): kiss and cuddle amorously the pair were snogging on the sofa : he snogged my girl at a party That same source notes that 'snogged up'-supposedly an RAF term dating to circa 1939-means 'Smartened up, 'all dressed up.'' Partridge 1945, 'Snog is perhaps a blend of snug and cod (to flatter or kid a person).' To be or go courting a girl to be or go love-making: RAF: since ca. However, Eric Partridge, A Dictionary of Slang and Unconventional English, Fifth Edition (1961) suggests a slightly different etymology: (Anderson) The term, esp as be or go snogging, seems to have orig in the RAF, late 1930s (Partridge 1945). Hence, to flirt, or to court, esp in be or come or go snogging: beatniks', adopted, ca. alteration of snug, cosy, notably as in that snuggling-up which so often preludes a warmer conjunction. 1977) very common throughout WW2 I surmise a dial. 'To make love with repletion of kissing and cuddling hence, snogging session, making love' (L.A. Paul Beale, ed., Partridge's Concise Dictionary of Slang and Unconventional English (1989) offers this entry for the verb snog:

Snogging book