I'm trying to understand how spelling works in Russian. Why does "томат" lack an "o" at the end, when some other words which I assume are derived from European loanwords, such as "пианино" or "метро", have an "о" at the end?
The English edition of Wiktionary lacked etymology info for "томат".
Why on Earth it should be? Just because in other languages -ato ending are OK for nouns? Why банан and not банана? Or кофе but not кофи?
This is emotional part of an answer, and as of the facts - well, it was derived from French tomate (which is something mentioned in Russian wiktionary by the way) and in French it was already pronounced pretty much the same way.
I guess the main question is why we are not pronouncing it like томатль - after all it was originally that way )))
Кофе matches at least the spelling in French, if not the pronunciation Кофе is a difficult compromise between Dutch (originally it was Кофий in Russian) and French.
Words get borrowed into the languages not necessarily from the languages they originated in, not necessarily keeping their meaning, not necessarily the way they originally sounded and not necessarily once.
In each separate case there is usually some kind of logic: e.g. you can trace step by step how Ancient Greek ἐλέφας (source of English "elephant") ultimately became Russian верблюд ("camel"), or how гиацинт and яхонт are both from a common Greek source, but it's an ad-hoc logic every time.
As for томат, банан etc., they were borrowed from French where they are pronounced in almost the same way as they are in Russian, and батат is most probably from Neapolitan or other southern Italian idiom.
Words borrowed from Spanish either directly or through English (торнадо, авокадо etc.) are neuter and indeclinable, and keep the final -о.
