watchtower (n.)

Old English wæccan "keep watch, be awake," from Proto-Germanic *wakjan, from PIE root *weg- "to be strong, be lively." Essentially the same word as Old English wacian "be or remain awake" (see wake (v.)); perhaps a Northumbrian form of it. Meaning "be vigilant" is from c. 1200. That of "to guard (someone or some place), stand guard" is late 14c. Sense of "to observe, keep under observance" is mid-15c. Related: Watched; watching.

Old English torr "tower, watchtower," from Latin turris "a tower, citadel, high structure" (also source of Old French tor, 11c., Modern French tour; Spanish, Italian torre "tower"), possibly from a pre-Indo-European Mediterranean language. Meaning "lofty pile or mass" is recorded from mid-14c. Also borrowed separately 13c. as tour, from Old French tur; the modern spelling (1520s) represents a merger of the two forms.