The term GASEOUS PREFIX refers to two words that are used as prefixes to describe something that is gaseous. The two words are AERI (4 letters) and AER (3 letters). AERI is derived from the Greek word for air, aer, and is used to describe something that is related to air or gas. AER is also derived from the Greek word for air, but is used to describe something that is made of air or gas. Both words are used to describe something that is gaseous in nature.