Summertime

wiktionary

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From Middle English somertime, equivalent to summer +‎ time. Compare Dutch zomertijd(“summertime”), German Sommerzeit(“summertime”), Danish sommertiden(“summertime”), Swedish sommartid(“summertime”). Compare summertide.

etymonline

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summertime (n.)

also summer-time, late 14c., somer tyme, from summer (n.1) + time (n.). Earlier were summertide (mid-13c.), sumeres tid (late Old English). In Britain, as two words, with reference to what in U.S. is daylight saving time, recorded from 1916.