The Collaborative International Dictionary of English v.0.48:

Oneness \One"ness\, n.
   The state of being one; singleness in number; individuality;
   unity.
   [1913 Webster]

         Our God is one, or rather very oneness.  --Hooker.
   [1913 Webster]

WordNet (r) 3.0 (2006):

oneness
    n 1: the quality of being united into one [syn: oneness,
         unity]

Moby Thesaurus II by Grady Ward, 1.0:

153 Moby Thesaurus words for "oneness":
   accord, accordance, affinity, agape, agreement, allness, amity,
   assent, bill, bonds of harmony, bone, brotherly love, buck,
   caritas, cement of friendship, charity, chorus, coequality,
   coherence, coincidence, collectivity, combination, communion,
   community, community of interests, compatibility, completeness,
   complex, concert, concord, concordance, conformance, conformation,
   conformity, congeniality, congruence, congruency, congruity,
   consistency, consonance, consort, cooperation, correspondence,
   differentiation, differentness, distinctiveness, egohood,
   elementarity, embodiment, empathy, entireness, entirety, equality,
   equivalence, esprit, esprit de corps, feeling of identity,
   fellow feeling, fellowship, fish, frictionlessness, frogskin,
   fundamentality, fusion, good vibes, good vibrations, happy family,
   harmony, homogeneity, homoousia, human factor, identity,
   indistinguishability, individualism, individuality, indivisibility,
   intactness, integer, integrality, integration, integrity,
   intersection, inviolability, irreducibility, kinship,
   like-mindedness, love, monism, mutuality, no difference,
   nominalism, nonconformity, organic unity, overlap, parallelism,
   particularism, particularity, peace, personal equation,
   personal identity, personality, personship, plainness, purity,
   rapport, rapprochement, reciprocity, sameness, self-consistency,
   self-identity, selfhood, selfness, selfsameness, severity, sharing,
   simpleness, simplicity, singleness, singularity, skin, smacker,
   solidarity, solidification, solidity, soul, starkness, symmetry,
   sympathy, symphony, sync, synchronism, synonymity, synonymousness,
   synonymy, tally, team spirit, timing, totality, unadulteration,
   understanding, undividedness, unification, uniformity, union,
   uniqueness, unison, unisonance, unity, univocity, unmixedness,
   unsophistication, whole, wholeness