apathy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Lack of interest or concern, especially regarding matters of general importance or appeal; indifference.
• noun Lack of emotion or feeling; impassiveness.

from The Century Dictionary.

• noun In the Stoic philos., a certain imperturbability produced in the wise man's soul by sincere rejection of the notion that pleasure is in itself desirable, or pain in itself undesirable and by trained watchfulness to exclude all unreasonable passions (all passions affecting conduct being regarded as unreasonable).
• noun Want of feeling; absence or suppression of passion, emotion, or excitement; insensibility; indifference.
• noun Synonyms Indifference, Insensibility, Impassibility, Apathy, Stoicism, Unconcern, Phlegm, Calmness, torpor, coldness, coolness, unfeelingness, lethargy, immobility. (See list under indifference.) Indifference denotes absence of feeling, passion, or desire toward a particular object: as, indifference to pain or ridicule. Apathy commonly implies a general want of feeling, a complete indifference in regard to anything, due to want of interest or attention, as in the case of a repressed or sluggish intellect, or of extreme illness or affliction. Insensibility and impassibility suggest the lack of capacity for feeling, or an absence of susceptibility, being qualities rather than states of mind. Indifference arising from impassibility relates more particularly to internal, that arising from insensibility to external, impressions; the former is, moreover, more profound and radical than the latter. Indifference may be an entirely proper state under the circumstances; insensibility and impassibility are always at least to be pitied; unconcern is always and indifference sometimes blameworthy, as cold and selfish. Stoicism is a studied suppression of feeling, or the concealment especially of painful feeling by force of will. Unconcern is absence of solicitude. (See care.) Phlegm most suggestive of physical temperament; it is a constitutional dullness or sluggishness, an incapability of being aroused by anything. Calmness is a tranquillity resulting from the mastery of the will over passions and feelings that perhaps are strong and keen, and hence is always commendable.

from the GNU version of the Collaborative International Dictionary of English.

• noun Want of feeling; privation of passion, emotion, or excitement; dispassion; -- applied either to the body or the mind. As applied to the mind, it is a calmness, indolence, or state of indifference, incapable of being ruffled or roused to active interest or exertion by pleasure, pain, or passion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Complete lack of emotion or motivation about a person, activity, or object; depression; lack of interest or enthusiasm; disinterest.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an absence of emotion or enthusiasm
• noun the trait of lacking enthusiasm for or interest in things generally