Watchful is an adjective meaning "keeping alert attention; observant and vigilant". Historically, it is from watch (Old English wæcce 'a watching', from wacian 'to be awake', from Proto-Germanic *wakaną) plus the adjective-forming suffix -ful. The visible construction is part of the etymology: watchful is not just an unanalyzed simple word. The modern meaning, "keeping alert attention; observant and vigilant", follows the base word through the added English ending. The historical chain links Old English wæcce, Old English wacian, and Proto-Germanic *wakaną. Close English family members include watchfully, watchfulness, watch, wake, and watcher.