The Collaborative International Dictionary of English v.0.48:

Propinquity \Pro*pin"qui*ty\, n. [L. propinquitas, from
   propinquus near, neighboring, from prope near.]
   [1913 Webster]
   1. Nearness in place; neighborhood; proximity.
      [1913 Webster]

   2. Nearness in time. --Sir T. Browne.
      [1913 Webster]

   3. Nearness of blood; kindred; affinity. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

propinquity
    n 1: the property of being close together [syn: proximity,
         propinquity]

Moby Thesaurus II by Grady Ward, 1.0:

88 Moby Thesaurus words for "propinquity":
   accord, addition, adjunct, affairs, affiliation, affinity,
   agnation, alliance, ancestry, approach, approximation, assemblage,
   association, blood, blood relationship, bond, brotherhood,
   brothership, closeness, cognation, combination, common ancestry,
   common descent, confines, connectedness, connection, consanguinity,
   contiguity, contiguousness, contrariety, convergence, cousinhood,
   cousinship, dealings, deduction, disjunction, enation, environs,
   fatherhood, filiation, foreground, fraternity, homology, immediacy,
   immediate foreground, intercourse, intimacy, junction, kindred,
   kinship, liaison, link, linkage, linking, maternity, matrilineage,
   matriliny, matrisib, matrocliny, motherhood, mutual attraction,
   nearness, neighborhood, nighness, paternity, patrilineage,
   patriliny, patrisib, patrocliny, precinct, proximity, purlieus,
   rapport, relatedness, relation, relations, relationship, sibship,
   similarity, sisterhood, sistership, sympathy, tie, tie-in,
   ties of blood, union, vicinage, vicinity



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

PROPINQUITY. Kindred; parentage. Vide. Affinity; Consanguinity; Next of kin.