What does the word acid mean?

Usage examples for acid

  1. It is practically pure phenylacetic acid, m. – Organic-Syntheses by Conant, James Bryant
  2. A 10 per cent acid phosphate is low- grade. – Crops and Methods for Soil Improvement by Alva Agee
  3. You may call it a jolly little adventure, but I call it the acid test. – The Prince of Graustark by George Barr McCutcheon