- Linguistics, Linguistic, and Linguist

Linguistics (noun) : The scientific study of language. (an academic discipline)

Linguistic (adjective) :
(1) The adjective from language, as in such phrases as ‘linguistic skill’
(2) The adjective from linguistics, where it refers to an approach characterized by the scientific attributes of that subject, as in ‘linguistic analysis’.

Linguist (noun) :
(1) A person who studies linguistics. For this meaning, the term Linguistician is
also used.

(2) Someone who speaks a large number of languages.
A linguist in the sense of a linguistics expert need not be fluent in languages, though he must have a wide experience of different types of languages