"Simmer Down" was the first single released by The Wailers, accompanied by the ska supergroup, The Skatalites, and produced by Clement "Coxsone" Dodd in 1963. It was the number one hit in Jamaica in February, 1964.

What means simmer down?

intransitive verb. 1 : to become calm or peaceful. 2 : to become reduced by or as if by simmering.

Where does the phrase simmer down come from?

simmer (v.)

Opposite sense, in simmer down, first recorded 1871, probably from the notion of moving from a full boil to a mere simmer. Related: Simmered; simmering. The noun meaning "a condition of simmering" is from 1809.