The Collaborative International Dictionary of English v.0.48:

Constituency \Con*stit"u*en*cy\
   (k[o^]n*st[i^]t"[-u]*[-e]n*s[y^]), n.; pl. Constituencies
   (k[o^]n*st[i^]t"[-u]*[-e]n*s[i^]z).
   A body of constituents, as the body of citizens or voters in
   a representative district.
   [1913 Webster]

WordNet (r) 3.0 (2006):

constituency
    n 1: the body of voters who elect a representative for their
         area

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "constituency":
   affiliates, ambit, associates, bailiwick, body of affiliates,
   citizenry, commonwealth, community, constituents,
   cultural community, dwellers, electoral college, electorate,
   electors, folk, footing, general public, habitancy, inhabitants,
   linguistic community, members, membership, nation, orbit, people,
   people at large, populace, population, public, society,
   speech community, sphere of influence, stamping ground, territory,
   turf, vantage, whole people