simmer down

Collins Concise English Dictionary © HarperCollins Publishers::

simmer down verb (adverb)

1. (intransitive) to grow calmer or quieter, as after intense rage or excitement
2. (transitive) to reduce the volume of (a liquid) by boiling slowly

WordReference Random House Learner's Dictionary of American English © 2025

sim•mer /ˈsɪmɚ/   v. 

1. Food to cook just below the boiling point: [no object]
   The sauce is simmering.
   [~ + object]
   Simmer the sauce.
2. to be in a state in which development, excitement, anger, etc., is present but held back:
   [no object] He was simmering with anger.
3. Slang Terms simmer down, [no object] to become calm or quiet:
   "Simmer down,'' I warned him.

n. [countable* usually singular]

4. the state or process of simmering:
   Cook to a slow simmer for fifteen minutes.

WordReference Random House Unabridged Dictionary of American English © 2025

sim•mer  (sim′ər), v.i. 

1. Food to cook or cook in a liquid at or just below the boiling point.
2. to make a gentle murmuring sound, as liquids cooking just below the boiling point.
3. to be in a state of subdued or restrained activity, development, excitement, anger, etc.:
   The town simmered with rumors.

v.t. 

4. to keep (liquid) in a state approaching boiling.
5. Food to cook in a liquid that is kept at or just below the boiling point.
6. simmer down:
   • to reduce in volume by simmering.
   • Slang Terms to become calm or quiet, as from a state of anger or turmoil:
     We waited for the audience to simmer down.

n. 

7. the state or process of simmering.

• ?
• alteration of earlier simper 1645–55

sim′mer•ing•ly, adv. 
Synonyms

• 3. See boil ¹.