Dictionary.com saves the day once again!
Corvette:
1. A fast, lightly armed warship, smaller than a destroyer, often armed for antisubmarine operations.
2. An obsolete sailing warship, smaller than a frigate, usually armed with one tier of guns.
Frigate:
1. A warship, usually of 4,000 to 9,000 displacement tons, that is larger than a destroyer and smaller than a cruiser, used primarily for escort duty.
2. A high-speed, medium-sized sailing war vessel of the 17th, 18th, and 19th centuries.
3. Archaic. A fast, light vessel, such as a sailboat.
Destroyer:
1. A small, fast, highly maneuverable warship armed with guns, torpedoes, depth charges, and guided missiles.
Cruiser:
1. One of a class of fast warships of medium tonnage with a long cruising radius and less armor and firepower than a battleship.
Battleship:
1. Any one of a class of warships of the largest size, carrying the greatest number of weapons and clad with the heaviest armor. Also called battlewagon.
Dreadnaught:
1. A battleship armed with six or more guns having calibers of 12 inches or more.
Juggernaut:
1. A massive inexorable force that seems to crush everything in its way
So there you go. Freespace is both right and wrong on some accounts (namely right with Corvettes, wrong with Cruisers, Frigates, and Destroyers).