Origin and history of tor

Middle English tour, "building lofty in proportion to its base width," usually free-standing, often used as a fortification or prison, from 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"), which is perhaps from a pre-Indo-European Mediterranean language.

The word in English was extended to any lofty pile or mass by mid-14c. It is also probably in part, from Old French tur. The modern English spelling with -w- is attested from c. 1400.

Often it is in specific reference to the Tower of London, which was The Tower by 1100. As a type of high headdress worn by women, c. 1600 (but the thing itself most popular at the end of that century).