Where does “Hapten” come from?

Hapten (German) comes from Ancient Greek ἅπτειν — present active infinitive of ἅπτω; to fasten.

Ancestry of “Hapten”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	ἅπτειν	present active infinitive of ἅπτω; to fasten

Hapten — Etymology, Origin & Word History | Etymology Explorer