also semiprofessional, 1824, in reference to one who is paid for an occupation or activity but does not rely on it for sustenance, from semi- + professional (adj.). As a noun from 1843. Related: Semi-professionally.
before vowels often sem-, a word-forming element of Latin origin meaning "half," also loosely, "part, partly; partial, almost; imperfect; twice," from Latin semi- "half," from PIE *semi- "half" (source also of Sanskrit sami "half," Greek hēmi- "half," Old English sam-, Gothic sami- "half").
The Old English cognate, sam-, was used in such compounds as samhal "in poor health, weakly," literally "half-whole;" samsoden "half-cooked" ('half-sodden'), figuratively "stupid" (compare half-baked); samcucu "half-dead," etymologically "half-alive" (see quick (adj.)); and the lingering survivor, sandblind "dim-sighted" (q.v.).
The Latin element was common in formations from Late Latin, as in semi-gravis "half-drunk," semi-hora "half hour," semi-mortuus "half-dead," semi-nudus "half-naked," semi-vir "half-man, hermaphrodite."
The Latin-derived form in English has been active in forming native words since 15c. Semi-bousi "half-drunk" ('semi-boozy'), now obsolete, was among the earliest (c. 1400). As a noun, semi has variously been short for semi-detached house (by 1912), semi-trailer (by 1942), semi-final (by 1942).
mid-15c., profeshinalle, in reference to the profession of religious orders; see profession. By 1747 of careers, "pertaining to or appropriate to a profession or calling" (especially of the skilled or learned trades from c. 1793); In sports and amusements, "undertaken or engaged in for money" (opposed to amateur), by 1846. Related: Professionally.
<a href="https://www.etymonline.com/word/semi-professional">Etymology of semi-professional by etymonline</a>
Harper, D. (n.d.). Etymology of semi-professional. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/semi-professional