Second-in-command is a title denoting that the holder of the title is the second-highest authority within a certain organisation. In the British Army or Royal Marines, the second-in-command is the deputy commander of a unit, from battalion or regiment downwards.

What is second-in-command?

Definition of second-in-command

: someone who is ranked second in a group or organization the police chief's second-in-command.

Is there a second-in-command?

A second-in-command is someone who is next in rank to the leader of a group, and who has authority to give orders when the leader is not there.