What's the difference between merchantman and merchantmen?

Merchantman

Definition:

• (n.) A merchant.
• (n.) A trading vessel; a ship employed in the transportation of goods, as, distinguished from a man-of-war.

Example Sentences:

• (1) The bottle was retrieved by Nato warships who were nearby after responding to an earlier call for help from the Italian merchantman.

Merchantmen

Definition:

• (pl. ) of Merchantman

Example Sentences: