botanist (n.)

"the science of plants," 1690s, from botanic. The -y is from astronomy, etc. Botany Bay in Australia was named by Captain Cook (1770) on account of the great variety of plants found there; later it was a convict settlement (1778).

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.