ACID

Sour to the taste (4)

Solution has appeared in 4 crosswords (2 across and 2 down):

• Quick crossword No 15,960 — 2021-07-01 23:00:21
  23A: Vinegary (4)
• Quick crossword No 15,728 — 2020-10-02 23:00:06
  20D: What turns blue litmus paper red (4)
• Quick crossword No 15,620 — 2020-05-29 23:00:26
  18A: LSD (4)
• Quick crossword No 15,222 — 2019-02-20 00:00:23
  18D: Sour to the taste (4)