late 14c., "to belong to as a possession or right," from Old French apendre (13c.) "belong, be dependent (on); attach (oneself) to; hang, hang up," and directly from Latin appendere "cause to hang (from something); weigh out," from ad "to" (see ad-) + pendere "to hang, cause to hang; weight; pay" (from PIE root *(s)pen- "to draw, stretch, spin").
Meaning "to hang on, attach as a pendant" is 1640s; that of "attach as an appendix" is recorded by 1843. OED says the original word was obsolete by c. 1500, and these later transitive senses thus represent a reborrowing from Latin or French. Related: Appended; appending.
word-forming element in nouns of act, process, function, condition, from Old French and French -age, from Late Latin -aticum "belonging to, related to," originally neuter adjectival suffix, from PIE *-at- (source of Latin -atus, past participle suffix of verbs of the first conjugation) + *-(i)ko-, secondary suffix forming adjectives (see -ic).
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Definitions of appendage from WordNet
an external body part that projects from the body;