Is it ensure, insure, or assure?
mid-15c., from Old French chien terrier "terrier dog," literally "earth dog," from Medieval Latin terrarius "of earth," from Latin terra "earth" (see terrain). So called because the dogs pursue their quarry (foxes, badgers, etc.) into their burrows.
"loop raised in pile-weaving, left uncut," 1784, possibly an alteration of French tiré "drawn," from past participle of tirer "draw out" (cf. German gezogener Sammet "drawn velvet").