
Base Words/Root Words
The main word.
Prefixes and suffixes are often added to the root word.
Suffix Examples:

jump
jumper
jumped
jumps
jumping

dance
dancer
danced
dances
dancing

Prefix Examples
reappear
disapprove
unclear
coexist
bicycle
anticeptic
exwife
http://www.uefap.com/vocab/build/building.htm