WordNet (r) 3.0 (2006):

monitoring
    n 1: the act of observing something (and sometimes keeping a
         record of it); "the monitoring of enemy communications
         plays an important role in war times"

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "monitoring":
   custodianship, custody, eagle eye, guard, guardedness,
   guardianship, interlaced scanning, invigilation, lookout, mixing,
   observance, peeled eye, proctoring, prudence, qui vive, scanning,
   shading, sharp eye, stewardship, surveillance, switching,
   telecasting, televising, vigil, vigilance, wariness, watch,
   watch and ward, watchful eye, watchfulness, watching,
   weather eye