The Collaborative International Dictionary of English v.0.48:
Seniority \Sen*ior"i*ty\, n. The quality or state of being senior. [1913 Webster]WordNet (r) 3.0 (2006):
seniority n 1: higher rank than that of others especially by reason of longer service [syn: seniority, senior status, higher status, higher rank] 2: the property of being long-lived [syn: longevity, seniority]