To render calm or quiet; to calm; to still; to appease.

To keep from motion, or stop the progress of, by the stilling of the wind; as, the fleet was becalmed.

A vessel is becalmed when the sails hang limp and lifeless because of no wind

When the wind is blocked by a cliff or other large object, or has died due to meteorological conditions, so that the sails hang slack and are deprived of power. It is possible to move a boat in these circumstances, by using the rolling caused by the sea or swell, to fill the sails on each roll, but it takes time and patience.