もっとも is a conjunction used to add a qualification, reservation, or caveat to a preceding statement. After making an assertion, もっとも introduces additional information that partially limits, corrects, or nuances what was just said. It translates naturally as "however," "though," "having said that," "mind you," or "although."
Unlike simple contrast conjunctions like でも or しかし, もっとも does not fully contradict the first statement – it acknowledges it while adding a condition or exception. It's like saying "that's true, but let me add this caveat."
もっとも typically appears at the beginning of a new sentence or clause, often followed by a comma. It is used in written language and somewhat formal speech, though it also appears in everyday conversation.
Note: This もっとも (尤も) is different from the superlative adverb もっとも最も (もっとも), meaning "most." Context and kanji make the distinction clear.