If one recalls the French expression so commonly heard during the recent World Wars, “C’est la guerre!” a clue may be seen for the origin of the word garret.
The ancient French spelling was guerite, and the term meant a watchtower or place of observation, as under the roof of a building where a sentry could be on the lookout for an approaching enemy.
Taken to England by the Norman conquerors, its original meaning became altered to our present sense and its spelling, thanks to similarity of pronunciation, transformed to garret.
