Where does “stagnatus” come from?

stagnatus (Latin) comes from Latin stagnō, from Latin stagnum, from Proto-Indo-European steh₂g- — to seep drip; to seep, drip.

Ancestry of “stagnatus”, step by step

Step	Language	Word	Meaning
1	Latin	stagnō	to cover the land as a lake; to become a pool; to stagnate
2	Latin	stagnum	pond, swamp, fen; any piece of standing water;...
3	Proto-Indo-European	steh₂g-	to seep drip; to seep, drip