The Collaborative International Dictionary of English v.0.48:
Langsyne \Lang`syne"\, adv. & n. [Scot. lang long + syne since.] Long since; long ago. [Scot.] [1913 Webster]WordNet (r) 3.0 (2006):
langsyne adv 1: at a distant time in the past (chiefly Scottish) n 1: past times remembered with nostalgia [syn: auld langsyne, langsyne, old times, good old days]