When I started to visit the West Indies I discovered its other meaning: a fruit of the genus Musa, similar to the banana. Scientifically, there is apparently no sharp difference between bananas and plantains: we tend to call them plantains if they are relatively large and eaten cooked, as a vegetable, and bananas otherwise. (The leftmost items in my picture are plantains. Don’t ask me where green bananas, eaten as a cooked vegetable in Jamaica, fit in.) Wikipedia says
Plantains tend to be firmer and lower in sugar content than dessert bananas. Bananas are most often eaten raw, while plantains usually require cooking or other processing, and are used either when green or unripe (and therefore starchy) or overripe (and therefore sweet).
According to the OED, plantain also has a third meaning (“now rare”), a plane tree.
Anyhow, this note is not about the meaning(s) of the word but about its pronunciation.
Although in LPD I prioritize ˈplæntɪn, I’ve always actually said ˈplɑːntɪn myself. So I would put the word in that subset of words that hover between the TRAP and BATH categories, with æ or ɑː in BrE, æ in AmE. (In AofE, page 135, this is set 59´, which includes other cases such as alas, exasperate and plaque.) In LPD I give the AmE pronunciation correspondingly as ˈplæntən (where ən stands for either syllabic n̩ or ən).
But in an American television program(me) I recently heard several people refer to it as a plænˈteɪn. I don’t know how prevalent this stressing is in the US: it’s not shown in the AmE dictionaries I have to hand. I suspect it’s a spelling pronunciation invented rather recently.
Intriguingly, the current Wikipedia entry not only gives this pronunciation for AmE but also, wrongly, attributes it to me!