Meaning of “command” - Learner’s Dictionary

command

noun uk us /kəˈmɑːnd/
CONTROL [ U ]

control over someone or something and responsibility for them:

The soldiers were under the command of a tough sergeant-major.
Jones was in command (= the leader).
ORDER [ C ]

B2 an order to do something

KNOWLEDGE [ no plural ]

B2 knowledge of a subject, especially a language:

She had a good command of French.
be at sb's command

to be ready to obey someone's orders

COMPUTER [ C ]

an instruction to a computer

(Definition of “command noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)