NOUN (2)

1. the feeling caused by disagreeable stimuli; one pole of a continuum of states of feeling;

2. the quality of giving displeasure;
- Example: "the recent unpleasantness of the weather"

The Collaborative International Dictionary of English v.0.48:

Unpleasant \Un*pleas"ant\, a.
   Not pleasant; not amiable or agreeable; displeasing;
   offensive. -- Un*pleas"ant*ly, adv. -- Un*pleas"ant*ness,
   n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unpleasantness
    n 1: the feeling caused by disagreeable stimuli; one pole of a
         continuum of states of feeling [ant: pleasantness]
    2: the quality of giving displeasure; "the recent unpleasantness
       of the weather" [ant: pleasantness, sweetness]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "unpleasantness":
   Discordia, Eris, badness, clash, clashing, conflict, contention,
   damnability, disaccord, disaffinity, discord, discordance,
   discordancy, disharmony, enmity, evilness, friction, improperness,
   inaccuracy, inauspiciousness, incompatibility, incompatibleness,
   inexpedience, inferiority, inharmoniousness, inharmony, invalidity,
   jangle, jar, malevolence, mischief, moral badness, noncooperation,
   open conflict, peccancy, reprehensibility, rub, strained relations,
   tension, unfavorableness, unharmoniousness, unhealthiness,
   unkindness, unskillfulness, viciousness, wickedness