/ ˌɔːld læŋ ˈsaɪn; NAmE / noun
an old Scottish song expressing feelings of friendship, traditionally sung at midnight on New Year's Eve
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WORD ORIGIN
late 18th cent.: Scots (from Scots auld old and archaic Scottish lang syne times gone by ). The phrase was popularized as the title and refrain of a song by Robert Burns (1788).