third mate

noun

the officer of a merchant vessel next in command beneath the second mate.

Also called third officer.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for third mate

Historical Examples of third mate

This set everybody in motion, and the captain and third-mate were on deck in a minute.
Afloat And Ashore
James Fenimore Cooper
As third-mate, it was my duty to see the boxes taken out of the hold, and the opium delivered.
Ned Myers
James Fenimore Cooper