1
: a sour substance
specifically
: any of various typically water-soluble and sour compounds that in solution are capable of reacting with a base (see base entry 1 sense 6a) to form a salt, redden litmus, and have a pH less than 7, that are hydrogen-containing molecules or ions able to give up a proton to a base, or that are substances able to accept an unshared pair of electrons from a base
2
: something incisive, biting, or sarcastic
a social satire dripping with acid
3
: lsd
acidy
adjective
ˈa-sə-dē
1
a
: sour, sharp, or biting to the taste
an acid flavor
b
: sharp, biting, or sour in manner, disposition, or nature
an acid individual
an acid personality
c
: sharply clear, discerning, or pointed
an acid wit
acid criticism
d
: piercingly intense and often jarring
acid yellow
2
a
: of, relating to, or being an acid
also
: having the reactions or characteristics of an acid
acid soil
an acid solution
b
of salts and esters
: derived by partial exchange of replaceable hydrogen
acid sodium carbonate NaHCO3
c
: containing or involving the use of an acid (as in manufacture)
an acid bath
d
: marked by or resulting from an abnormally high concentration of acid
acid indigestion
3
: relating to or made by a process in which the furnace is lined with acidic material and an acidic slag is used
acid steel
4
: rich in silica
acid rocks
acidly
adverb
acidness
noun
Examples of acid in a Sentence
Noun
the acids in your stomach
the kinds of acid found in your stomach
Adjective
He washes his windows with an acid solution of vinegar and water.
with her acid personality, my aunt could be relied upon to bring some much-needed balance to the holiday gush
Recent Examples on the Web
Em Sauter, Forbes.com, 13 May 2025
According to Thomas, tranexamic acid is used topically for treating pigmentation and inflammatory redness.
—Tracy Achonwa, Vogue, 8 May 2025
Hannah Yasharoff, USA Today, 19 Apr. 2025
Gastrointestinal Symptoms Fish oil may stimulate acid production in the stomach, which can cause heartburn or indigestion—especially if taken on an empty stomach.
—Amy Brownstein, Ms, Rdn, Verywell Health, 7 Apr. 2025
See All Example Sentences for acid
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
Send us feedback.
Noun
These apples have enough acids, tannins, sweetness, and body to stand on its own as a single varietal.
—Em Sauter, Forbes.com, 13 May 2025
According to Thomas, tranexamic acid is used topically for treating pigmentation and inflammatory redness.
—Tracy Achonwa, Vogue, 8 May 2025
Adjective
Also, eating large quantities of food can lead to increase acid production and acid reflux.
—Hannah Yasharoff, USA Today, 19 Apr. 2025
Gastrointestinal Symptoms Fish oil may stimulate acid production in the stomach, which can cause heartburn or indigestion—especially if taken on an empty stomach.
—Amy Brownstein, Ms, Rdn, Verywell Health, 7 Apr. 2025
See All Example Sentences for acid
Cite this Entry
“Acid.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/acid. Accessed 23 May. 2025.
Copy CitationKids Definition
acid
2 of 2 noun1
: a sour substance
2
: a compound that usually dissolves in water, has a sour taste, reacts with a base to form a salt, and turns litmus paper red
3
: lsd
Medical Definition
acid
1 of 2 noun1
: a sour substance
specifically
: any of various typically water-soluble and sour compounds that in solution are capable of reacting with a base (see base sense 3a) to form a salt, redden litmus, and have a pH less than 7, that are hydrogen-containing molecules or ions able to give up a proton to a base, or that are substances able to accept an unshared pair of electrons from a base
2
: lsd
acid
2 of 2 adjective
ac·id
ˈas-əd 
1
: sour, sharp, or biting to the taste
2
a
: of, relating to, or being an acid
also
: having the reactions or characteristics of an acid
an acid solution
b
of salts and esters
: derived by partial exchange of replaceable hydrogen
acid sodium carbonate NaHCO3
c
: marked by or resulting from an abnormally high concentration of acid
acid indigestion
see also acid reflux
Love words? Need even more definitions?
Merriam-Webster unabridged
Share