-ologist

Etymology tree
Ancient Greek -ο- (-o-)der.
Latin -o-bor.
English -o-
Proto-Indo-European *leǵ-
Ancient Greek λόγος (lógos)
Proto-Indo-European *-h₂
Proto-Indo-European *-éh₂
Proto-Indo-European *-i-eh₂
Proto-Hellenic *-íā
Ancient Greek -ῐ́ᾱ (-ĭ́ā)
Ancient Greek -λογῐ́ᾱ (-logĭ́ā)bor.
Latin -logialbor.
French -logiebor.
English -logy
Proto-Indo-European *-id-
Proto-Indo-European *-yéti
Proto-Indo-European *-idyéti
Proto-Hellenic *-íďďō
Ancient Greek -ῐ́ζω (-ĭ́zō)
Proto-Hellenic *-tās
Ancient Greek -τής (-tḗs)
Ancient Greek -ῐστής (-ĭstḗs)bor.
Latin -istader.
Old French -istebor.
Middle English -ist
English -ist
English -logist
English -ologist
From -o- + -logist.