(UK, military, nautical, historical) A second-rate ship of the line.

Somebody ranking next below a commander. / Someone ranking next below the person in charge.

plural of second cousin

belonging to the second string of a team / substitute or replacement / second most important

(physics) A wave of fluctuating temperature or entropy propagated in the superfluid phase of liquid helium

The upper joint of the leg of a fowl, especially when used as food

(biochemistry) Any substance used to transmit a signal within a cell, especially one which triggers a cascade of events by activating cellular components

(neutral or mildly positive connotation) Of a standard or grade one level below the best. / (negative connotation) Inferior in quality or standing.

The second gearing available from a gearbox. / (idiomatic, figuratively) Mediocre, sluggish performance.

An angle, one sixtieth (1/60th) of a minute of arc or one 3600th of a degree.