"Word" as a unit of language

"Words" are the units. Depending on what you're referring to, sounds are also units of language, as are sentences. In linguistics, it's a bit more involved than that, though.

Are you asking for the definition of the word "unit?"

"An individual, group, structure, or other entity regarded as an elementary structural or functional constituent of a whole."

Nat I'd immediately respond, 'noun'

A word is one part of expression, known as language.

Punk that one's got me, for one, goin'. I'm not exactly sure but I might edit as

A word is one part of an expression known as language

..since there are probably many other kinds of expression

Guys, help....,