Question

acid
ac·id
I
 /ˈæsəd/  noun  ,  pl   acids
  1 chemistry : a chemical with a sour taste that forms a salt when mixed with a base
   [  count  ] the acids in your stomach
   [  noncount  ] the kinds of acid found in your stomach
   ◇ An acid has a pH of less than 7. Very strong acids are able to burn holes in things. — compare base 6, 1, PH
  2 [  noncount  ] slang : lsd
   His friend dropped acid [=took LSD] at the concert.
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II
  adj   [more ~; most ~]
  1 always used before a noun : of, relating to, or having the qualities of an acid
   He washes his windows with an acid solution of vinegar and water.
   an acid [=sour] taste
   This kind of plant grows well in acid [=acidic] soil.
   Their pizza gives me acid indigestion. [=a burning feeling in the stomach]
  2 : sharp, strong, and critical in tone
   He made some very acid [=biting, caustic] comments.
   acid remarks
  acid·i·ty /əˈsıdəti/  noun   [  noncount  ]
   They measured the acidity of the soil.
   the acidity [=tartness, sourness] of lemon juice
  ac·id·ly  adv  
   She acidly refers to her former husband as “that little man.”