The basic part of a word that is also the source of its essential meaning is called a

subject.
prefix.
root.
suffix.

root - the basic part of a word
example: reCONSTRUCTion

prefix - an addition before the root of a word
example: REconstruction

suffix - an addition at the end of the root of a word
example: reconstructION

The root is what contributes to the basic meaning of a word - prefixes and suffixes serve to narrow down the meaning - who, when, how, in what tense
example: re - again
construct - to build
ion - the action of

So the word RECONSTRUCTION would mean "the action of building again."

Hope that helped! Good luck! :)

P.S. Although you didn't ask for it, the subject is the object in the sentence that is performing the predicate
example: The girl ran to the store.
girl - subject
ran - predicate

It doesn't really have much in common with roots, prefixes and suffixes, all which are similar in function Source(s): Teaching English