Ultimately from Ancient Greek γῆ (gê, “earth”) + λόγος (lógos, “speech, oration, study”), likely via Slavic languages (cf. Polish geolog, Russian гео́лог (geólog), Ukrainian гео́лог (heóloh)).
געאָלאָג • (geolog) m, plural געאָלאָגן (geologn), feminine געאָלאָגין (geologin)