1845, "state of being bored," from bore (v.1) + -dom. It also has been employed in a sense "bores as a class" (1849) and "practice of being a bore" (1840, a sense properly belonging to boreism, 1833).
Entries linking to boredom
bore v.1
"pierce or perforate with a rotatory cutting instrument, make a circular hole in by turning an auger, drill, etc.," Old English borian "to bore through, perforate," from bor "auger," from Proto-Germanic *buron (source also of Old Norse bora, Swedish borra, Old High German boron, Middle Dutch boren, German bohren), from PIE root *bhorh- "hole."
-dom
abstract suffix of state, from Old English dom "statute, judgment" (see doom (n.)). Originally an independent word, but already active as a suffix in Old English (as in freodom, wisdom). Cognate with German -tum (Old High German tuom). "Jurisdiction," hence "province, state, condition, quality."