I. (ˈ)laŋˈzīn, (ˈ)laiŋ-, -ˈsīn adverb (or adjective)
Etymology: Middle English (Scots) lang sine, from lang long + sine, syne since — more at long , syne
chiefly Scotland : at a distant time in the past
II. noun
chiefly Scotland : times past : old times
old men sat … and talked politics, racing, or lang syne — Ruth Park