"a student of the science of life," 1813, from biology + -ist. Earliest use is in reference to human life (with the Greek sense of bios); in its modern scientific sense by 1874. Biologian is attested from 1865.
"the science of life and living things," 1819, from Greek bios "life, one's life, lifetime" (from PIE root *gwei- "to live;" see bio-) + -logy "study of." Suggested 1802 by German naturalist Gottfried Reinhold Treviranus, and introduced as a scientific term that year in French by Lamarck; they seem to have hit upon the word independently.
word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.
Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.
<a href="https://www.etymonline.com/word/biologist">Etymology of biologist by etymonline</a>
Harper, D. (n.d.). Etymology of biologist. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/biologist