bound form

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A linguistic element that always occurs as part of another word, such as –ly in lovely.
• noun The form taken by a noun in a Semitic language when the noun is followed directly by a possessor noun or by a possessive pronoun suffix.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun linguistics a unit of language that can be only be used as part of a word, not as a word on its own (such as the English suffix -ly)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a morpheme that occurs only as part of a larger construction; eg an -s at the end of plural nouns