Latin word decimo comes from Latin decima (Tenth hour. Tenth part. Tithe.), Latin -one(-onem|m)

Detailed word origin of decimo

Dictionary entry	Language	Definition
decima	Latin (lat)	Tenth hour. Tenth part. Tithe.
-one(-onem|m)	Latin (lat)
decimo	Latin (lat)	To decimate (select every tenth person for punishment). To pay tithes.