The only published book about Montserratian speech, George Irish’s Alliouagana Folk (Plymouth: Jagpi, 1985), is a collection of local proverbs, sayings, words and phrases. It duly records this word in its glossary.
santipee - centipedeRichard Allsopp’s scholarly Dictionary of Caribbean English Usage (OUP 1996) also records this pronunciation of the word (though with a different medial vowel) as common to the entire Caribbean English Creole region, and speculates about its origin as Portuguese.I can see that a Portuguese source could explain the loss of the final consonant — though this could also be due to the characteristic Creole uncertainty about final d (compare for instance galvanize meaning ‘corrugated metal roofing’, shortened from galvanized iron). Apart from that, though, I would have thought that Portuguese centopeia, phonetically sẽtoˈpeja, does not seem on phonetic grounds to be a more likely source than a straightforward English origin. (OK, English got it via French from Latin centipeda ‘hundred-foot’, as did the Portuguese.)