dam (n.1)

"water barrier," early 14c., probably from Old Norse dammr or Middle Dutch dam, both from Proto-Germanic *dammaz (source also of Old Frisian damm, German Damm), which is of unknown origin.

dam (n.2)

"animal mother," c. 1300, variant of dame (q.v.), also originally used, like that word, for "lady, mother;" but meanings diverged into separate spellings by 16c.

dam (v.)

late 15c., from dam (n.1). Related: Dammed; damming.