Where does “ōrātōrī” come from?

ōrātōrī (Middle English) comes from Old French orator, from Latin oratorium, from Latin oratorius, from Latin orator, from Latin orare, from Latin oro, from Latin os, from Proto-Italic ōs — bone.

Ancestry of “ōrātōrī”, step by step

ōrātōrī traces back through 3 separate lines of ancestry.

via Old French orator

Step	Language	Word	Meaning
1	Old French	orator	—
2	Latin	oratorium	nominative neuter singular of ōrātōrius;...
3	Latin	oratorius	oratorical
4	Latin	orator	an orator, speaker; a spokesman, spokesperson; an...
5	Latin	orare	present active infinitive of ōrō; second-person...
6	Latin	oro	I orate, deliver a speech; I plead, beg; I pray,...
7	Latin	os	mouth; face, appearance, head; speech
8	Proto-Italic	ōs	mouth
9	Proto-Indo-European	h₃ésth₁	bone

via Old French oratur

Step	Language	Word	Meaning
1	Old French	oratur	—
2	Latin	ōrātōrium	—
3	Latin	ōrātōrius	oratorical
4	Latin	-tōrius	ory
5	Latin	-tor	-er
6	Proto-Italic	-tōr	Forms agent nouns to verb stems
7	Proto-Indo-European	-tōr	Derives agent nouns from verbs, denoting someone...
8	Proto-Indo-European	-tor-s	—

via Old French oratour

Step	Language	Word	Meaning
1	Old French	oratour	—

Every word from Proto-Indo-European h₃ésth₁ →Every word from Proto-Italic ōs →Every word from Latin os →