*ater-

"melancholic," 1725, from Medieval Latin atrabilarius; an alternative of atrabilious (q.v.). Other alternatives are, or were, atrabilarious (1680s), atrabilarian (1670s), atrabilaric (1620).

"affected by melancholy," 1650s, from Latin atra bilis, translating Greek melankholia "black bile" (see melancholy; also compare bile). Atra is fem. of ater "black, dark, gloomy," and is perhaps "blackened by fire," from PIE root *ater- "fire." Related: Atrabiliousness.