1) N-COUNT: with supp The chief of an organization is the person who is in charge of it.

...a commission appointed by the police chief.

...Putin's chief of security.

2) N-COUNT; N-TITLE The chief of a tribe is its leader.

...Sitting Bull, chief of the Sioux tribes of the Great Plains.

3) ADJ: ADJ n Chief is used in the job titles of the most senior worker or workers of a particular kind in an organization.

...the chief test pilot.

4) ADJ: ADJ n The chief cause, part, or member of something is the most important one.

Financial stress is well established as a chief reason for divorce...

The job went to one of his chief rivals.

main, principal

English dictionary. 2008.