The Collaborative International Dictionary of English v.0.48:

Relinquishment \Re*lin"quish*ment\ (-ment), n.
   The act of relinquishing.
   [1913 Webster]

WordNet (r) 3.0 (2006):

relinquishment
    n 1: a verbal act of renouncing a claim or right or position
         etc. [syn: relinquishment, relinquishing]
    2: the act of giving up and abandoning a struggle or task etc.
       [syn: relinquishment, relinquishing]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "relinquishment":
   abandonment, abdication, abeyance, abjuration, abjurement,
   breakoff, capitulation, cease, ceasing, cessation, cession, close,
   closing, cold storage, demission, deposal, desinence, desistance,
   discontinuance, discontinuation, dropping out, emeritus status,
   forbearance, forced resignation, forswearing, giving in,
   giving over, giving up, handing over, nonexercise, recedence,
   recession, renouncement, renunciation, resignation, retiral,
   retirement, retreat, shutdown, stopping, superannuation, surcease,
   surrender, suspension, termination, voluntary resignation, waiver,
   withdrawal, withdrawing, yielding



Bouvier's Law Dictionary, Revised 6th Ed (1856):

RELINQUISHMENT, practice. A forsaking, abandoning, or giving over a right;
for example, a plaintiff may relinquish a bad count in a declaration, and
proceed on the good: a man may relinquish a part of his claim in order to
give a court jurisdiction.