Source : Webster's Revised Unabridged Dictionary (1913)

Langsyne \Lang`syne"\, adv. & n. [Scot. lang long + syne since.]
   Long since; long ago. [Scot.]

Source : WordNet®

langsyne
     n : past times remembered with nostalgia [syn: {auld langsyne},
         {old times}, {the good old days}]

langsyne
     adv : at a distant time in the past (chiefly Scottish)