early 14c., from Old French austere "strict, severe, harsh, cruel" (13c., Modern French austère) and directly from Latin austerus "dry, harsh, sour, tart," from Greek austeros "bitter, harsh," especially "making the tongue dry" (originally used of fruits, wines), metaphorically "austere, harsh," from PIE root *saus- "dry" (see sere (adj.)).
From late 14c. as "severe, rigid;" 1590s as "unadorned, simple in style, without luxuries;" 1660s as "grave, sober." Classical literal sense "sour, harsh" (1540s) is rare in English. Related: Austerely; austereness.