grief

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

• noun Deep mental anguish, as that arising from bereavement, or an instance of this. synonym: regret.
• noun A source or cause of deep mental anguish.
• noun Annoyance or frustration, or an instance of this.
• noun Trouble or difficulty, or an instance of this.
• noun Informal Criticism or rude talk.
• noun Archaic A grievance.

from The Century Dictionary.

• noun Regretful or remorseful sorrow; mental distress or misery caused by something done or suffered by one's self or others; affliction; woe.
• noun Cause of sorrow or pain; that which afflicts or distresses; grievance.
• noun Bodily pain; physical suffering.
• noun Synonyms Sorrow, Wretchedness, etc. (see affliction); bitterness, heartache, anguish, agony, woe.

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

• noun Pain of mind on account of something in the past; mental suffering arising from any cause, as misfortune, loss of friends, misconduct of one's self or others, etc.; sorrow; sadness.
• noun Cause of sorrow or pain; that which afficts or distresses; trial; grievance.
• noun rare Physical pain, or a cause of it; malady.
• noun [Colloq.] to meet with calamity, accident, defeat, ruin, etc., causing grief; to turn out badly.

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

• noun countable Cause or instance of sorrow or pain; that which afflicts or distresses; trial.

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

• noun something that causes great unhappiness
• noun intense sorrow caused by loss of a loved one (especially by death)