2018-2-4 · 1) The most used word by x is y. Or: The word most used by x is y. OK. 2) The word swag, mostly used by American teenagers, is [whatever]. The way it is written in the question is wrong. The most used = is the superlative, the most used word. mostly used-mostly is an adverb that modifies used. For example, this word is mostly used by truck drivers.