The Collaborative International Dictionary of English v.0.48:

Insistence \In*sist"ence\, n.
   The quality of insisting, or being urgent or pressing; the
   act of dwelling upon as of special importance; persistence;
   urgency.
   [1913 Webster]

WordNet (r) 3.0 (2006):

insistence
    n 1: continual and persistent demands [syn: insistence,
         insisting]
    2: the state of demanding notice or attention; "the insistence
       of their hunger"; "the press of business matters" [syn:
       imperativeness, insistence, insistency, press,
       pressure]
    3: the act of insisting on something; "insistence on grammatical
       correctness is a conservative position" [syn: insistence,
       insistency]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "insistence":
   abetment, application, assiduity, assiduousness, bulldog tenacity,
   concentration, constancy, demandingness, diligence,
   dogged perseverance, doggedness, encouragement, endurance,
   engrossment, exigency, fidelity, goading, importunacy,
   importunateness, importunity, indefatigability, industriousness,
   industry, insistency, instance, loyalty, needling, obstinacy,
   patience, patience of Job, permanence, perseverance, persistence,
   persistency, pertinaciousness, pertinacity, plodding, plugging,
   preoccupation, pressing, pressingness, pressure, pricking,
   prodding, relentlessness, resolution, sedulity, sedulousness,
   single-mindedness, singleness of purpose, slogging, spurring,
   stability, stamina, staying power, steadfastness, steadiness,
   stick-to-itiveness, stubbornness, tenaciousness, tenacity,
   tirelessness, unremittingness, unswerving attention, urgency,
   urging