What is the X in X-mas?
"water barrier," early 14c., probably from Old Norse dammr or Middle Dutch dam, both from Proto-Germanic *dammaz (cf. Old Frisian damm, German Damm), of unknown origin.
"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.
late 15c., from dam (n.1). Related: Dammed; damming.
A barrier against the passage of liquid or loose material, especially a rubber sheet used in dentistry to isolate one or more teeth from the rest of the mouth.
Dam (dām, däm), (Carl Peter) Henrik. 1895-1976.
Danish biochemist. He shared a 1943 Nobel Prize for the discovery of vitamin K.