MOST

Most has meanings which do not take the definiteRelating to a specific or determined person, thing, idea or time. E.g.: I know the guy you are talking about. ("the guy you are talking about") articleAny of the words "a", "an" and "the", used to limit or give definiteness to a noun. "A" and "an" are indefinite articles, while "the" is a definite article. E.g.: A man was standing on the platform. ("a", "the") the:

I’ve just read a most interesting book. (= I’ve just read a very interesting book.)
That was most kind of you. (= That was very kind of you.)
Most people who lose weight regain it in a very short time. (= The majority of the people who lose weight regain it in a very short time.)

ONLY

When only is used as an adjectiveA part of speech that modifies, qualifies or restricts a noun or a pronoun. E.g.: The apples are ripe. ("ripe"), it is preceded by the.

The only thing I hate about winter is the cold.

The definite article with ordinal numbers and with superlative adjectives
The definite article with ordinal numbers and with superlative adjectives The definite article with adjectives