enclitic

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

• noun A clitic that is attached to the end of another word. In Give 'em the works, the pronoun 'em is an enclitic.
• noun A clitic.
• adjective Of or relating to an enclitic or enclisis; forming an accentual unit with the preceding word.

from The Century Dictionary.

• Leaning on or against something else.
• Specifically
• In grammar, subjoined and accentually dependent: said of a word or particle which in regard to accent forms a part of a preceding word and is treated as if one with it, or gives up its separate accent, sometimes affecting that of its predecessor.
• In obstetrics, opposed to synclitic (which see).
• noun In grammar, a word accentually connected with a preceding word, as que (and) in Latin: arma virumque, arms and the man.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Gram.) A word which is joined to another so closely as to lose its proper accent, as the pronoun thee in prithee (pray thee).
• adjective (Gram.) Affixed; subjoined; -- said of a word or particle which leans back upon the preceding word so as to become a part of it, and to lose its own independent accent, generally varying also the accent of the preceding word.

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

• noun linguistics A clitic which phonetically joins with the preceding word. In English, the possessive 's is an example.
• adjective grammar Affixed phonetically.