Recently, someone asked about the difference between a sound (such as Puget Sound) and a bay (such as San Fransisco Bay).  Here's what Wikipedia says: 
A bay is an area of water bordered by land on three sides. 
A bight is a large (and often only slightly receding) bay. 
A gulf is a part of a lake or ocean that extends so that it is surrounded by land on three sides. 
A fjord is a narrow inlet of the sea between cliffs or steep slopes. 
A sound is a large sea or ocean inlet larger than a bay, deeper than a bight, wider than a fjord, or it may identify a narrow sea or ocean channel between two bodies of land. 
A bay generally occupies an area wider than a fjord but smaller than a sound or gulf, either of which may include one or more bays. 
Twice in the past 6 months, I've learned and forgotten the difference between a state and a commonwealth.  Here's what Wikipedia says: 
A state is one of the 50 entities of the United States. 
A commonwealth is an area/region that has a "government based on the common consent of the people" as opposed to one legitimized through their earlier Royal Colony status that was derived from the King of England.  This designation, which has no constitutional impact, applies to Kentucky, Massachusetts, Pennsylvania, and Virginia. 
A commonwealth (insular area) is an organized territory or colony that has established with the Federal Government a more highly developed relationship, usually embodied in a written mutual agreement.  This designation applies to the Northern Mariana Islands and Puerto Rico. 
I continually confuse the following two words, though they have completely different (opposite) meanings: 
Condemn:  To express strong disapproval of. 
Condone:  To overlook, forgive, or disregard (an offense) without protest or censure. 
#language