1.  singleness(n = noun.attribute) straightforwardness - without hypocrisy; "the singleness of his motives could not be questioned"
is a kind of sincerity

2.  singleness(n = noun.attribute) - the quality of concentrating on one central objective; "his singleness of purpose"
is a kind of assiduity, assiduousness, concentration
Derived form adjective single₇

1.  The quality or state of being single, or separate from all others; the opposite of doubleness, complication, or multiplicity. [1913 Webster]

2.  Freedom from duplicity, or secondary and selfish ends; purity of mind or purpose; simplicity; sincerity; as, singleness of purpose; singleness of heart. [1913 Webster]

N  celibacy, singleness, single blessedness, bachelorhood, bachelorship, misogamy, misogyny, virginity, pucelage, maidenhood, maidenhead, unmarried man, bachelor, Coelebs, agamist, old bachelor, misogamist, misogynist, monogamist, monk, unmarried woman, spinster, maid, maiden, virgin, feme sole, old maid, bachelor girl, girl-bachelor, nun, unmarried, unwed, unwedded, wifeless, spouseless, single.