Where does “transactivation” come from?

Transactivation comes from English trans- combined with activation, ultimately deriving from Proto-Indo-European terh₂- meaning to cross or overcome.

transactivation (English): The activation of something by another entity...

Definitions

Step	Language	Word	Meaning
1	English	activation	Making active and effective; bringing into a...
2	English	active	Having the power or quality of acting; causing...
3	Middle English	actyf	active, reactive
4	Old French	actif	active
5	Latin	āctīvus	active
6	Ancient Greek	ἐνεργητικός	Able to act on; acting on; Active; In the active...
7	Ancient Greek	ἐνεργέω	to be in action or activity, to operate; to...
8	Ancient Greek	ἐνεργός	at work, active
9	Ancient Greek	ἐν-	in, within; on
10	Ancient Greek	ἐν	in, on, at; among; in, at, or during the time of
11	Ancient Greek	δέρμα	skin, hide
12	Ancient Greek	γλυφή	carving, carved work; hole cut
13	Ancient Greek	-ῐ́ᾱ	{{l\|en\|-ia}}; "suffix forming abstract feminine...
14	Proto-Indo-European	-íh₂	—