The word “linguist” has two meanings.
The most commonly known meaning is “someone who speaks multiple languages”. A fancy synonym for this is “polyglot”.
The other meaning of “linguist” refers to a practitioner of a profession: A linguist is a scientific researcher who engages in the systematic study of language—a linguist does linguistics. We make observations about how language works, formulate hypotheses, test them, and revise our theories accordingly. We study language at all sorts of levels: linguistic sound systems, word structures, sentence structures, how words and sentences convey meanings, and how speakers use those meanings in the world. Some of us run psychological experiments in the lab, some of us travel around the world to study understudied languages, some of us take pictures of the brain while people are processing language, some of us study how babies acquire language, and some of us study dialectal differences and how societal factors impact them. Linguistics is widely considered to be one of the core fields of cognitive science, since our linguistic capacities are a key aspect of human cognition.
While many linguistic researchers are polyglots, most polyglots are not linguistic researchers.
You can get a sense of how linguists think about language here: http://languagelog.ldc.upenn.edu/nll/.
A linguist = λx : x is some form of coffee . linguistics papers
This is a riff on the Alfred Renyi quote: “A mathematician is a machine for turning coffee into theorems.” It is a function written in the quasi-mathematical lambda notation common among contemporary linguistic semanticists. To the semanticists out there, note the lack of interpretation brackets—I’m not saying that this function represents the meaning of the word “linguist”, I’m saying that a linguist just is a function that maps coffee to ling papers lol.