A convoy is a series of trucks or wagons traveling together. Here are some sentences.
There's a convoy of military vehicles approaching the compound, sir.
A destroyer convoyed the merchant ship.
The convoy was en route to Iraq.
The convoy lead the President to the White House safely.
Look at the convoy of Amish people in wagons.
Convoy is a noun.
All pegistrants move aside when they saw a convoy approaching
The military vehicles traveled through town in a convoy system.
The word 'convoy' IS a noun, a singular, common noun; a word for a group of ships or vehicles traveling together, often for mutual support or accompanied by a protective force. The noun 'convoy' is a word for a thing.
The plural of convoy is convoys. It is perfectly regular: just add an s.
caravan, Convoy
The officer escorted me to my cell.They escorted the humanitarian convoy through the crisis zone.