1530s, "a running (usually at full speed), a course" (especially of the sun, etc., across the sky), from French carriere "road, racecourse" (16c.), from Old Provençal or Italian carriera, from Vulgar Latin *(via) cararia "carriage (road), track for wheeled vehicles," from Latin carrus "chariot" (see car). Sense of "general course of action or movement" is from 1590s, hence "course of one's public or professional life" (1803).
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.
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Definitions of careerist from WordNet
a professional who is intent on furthering his or her career by any possible means and often at the expense of their own integrity;