Where does “strenuus” come from?

strenuus (Latin) comes from Proto-Indo-European (s)treg- — rigid, stiff; to be stiff, rigid, strong.

Ancestry of “strenuus”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	(s)treg-	rigid, stiff; to be stiff, rigid, strong

strenuus — Etymology, Origin & Word History | Etymology Explorer