Lewis & Short

pĕr-ăcerbus, a, um, adj., very harsh to the taste.

  1. I. Lit.: uva peracerba gustatu, Cic. Sen. 15, 53.
  2. II. Trop., very painful: mihi peracerbum fuit, quod, etc., Plin. Ep. 6, 5, 6.