Where does “doktor” come from?

doktor (Bikol Central) comes from Spanish doctor, from Latin doctor, from Latin -tor, from Proto-Italic -tōr, from Proto-Indo-European -tōr, from Proto-Indo-European -tor-s.

Ancestry of “doktor”, step by step

Step	Language	Word	Meaning
1	Spanish	doctor	doctor; physician
2	Latin	doctor	teacher, instructor; catechist
3	Latin	-tor	-er
4	Proto-Italic	-tōr	Forms agent nouns to verb stems
5	Proto-Indo-European	-tōr	Derives agent nouns from verbs, denoting someone...
6	Proto-Indo-European	-tor-s	—

Every word from Proto-Indo-European -tor-s →Every word from Latin -tor →Every word from Latin doctor →