Sync

google

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1920s: abbreviation.

wiktionary

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Clipping of  synchronization. 

etymonline

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sync (n.)

also synch, 1929, shortened form of synchronization (see synchronize). Originally in reference to soundtracks and pictures in the movies. Sense of "synchronization, harmony, agreement" first recorded 1961 in in sync. As a verb, short for synchronize, by 1945.