Watchful

wiktionary

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From Middle English waccheful, equivalent to watch +‎ -ful. Compare West Frisian waaks(“watchful”), Dutch waaks, waakzaam(“watchful”), German wachsam(“watchful”), Swedish vaksam(“watchful”).

etymonline

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watchful (adj.)

c. 1500, waccheful, from watch (v.) + -ful. Related: Watchfulness.