1932, alteration of dialectal verb smouch "to kiss" (1570s), possibly imitative of the sound of kissing (cf. German dialectal schmutzen "to kiss"). An earlier alteration produced smudge (v.) "to kiss, caress" (1844). Related: Smooched; smooching. As a noun by 1942.
: I'd rather have hooch, and a bit of a smooch
[the pilfering sense probably derives from the kissing sense by way of mooch; the kissing sense may be fr German schmutzen, ''to kiss, to smile''; the dated instance is spelled smouch; the term was reestablished as smooch in the 1930s]