Etymology
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unhappiness (n.)
late 15c., "misfortune," from unhappy + -ness. Meaning "mental misery" is from 1722.
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infelicity (n.)
late 14c., "unhappiness," from Latin infelicitas "bad luck, misfortune, unhappiness," from infelix (genitive infelicis) "unfruitful, barren; unfortunate, unhappy; causing misfortune, unlucky," from in- "not, opposite of" (see in- (1)) + felix "happy" (see felicity). Meaning "inappropriateness, unhappiness as to occasion" is from 1610s.
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embitter (v.)

"make bitter," c. 1600, from em- (1) + bitter (adj.). Now rare in its literal sense; figurative meaning "affect with bitterness or unhappiness" is attested by 1630s. Related: Embittered; embitterment.

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misery (n.)

late 14c., "state of grievous affliction, condition of external unhappiness," from Old French misere "miserable situation, misfortune, distress" (12c.), from Latin miseria "wretchedness," from miser "wretched, pitiable" (see miser). Meaning "condition of one in great sorrow or mental distress" is from 1530s.

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pain (v.)

c. 1300, peinen, "to exert or strain oneself, strive; endeavor," from Old French pener (v.) "to hurt, cause pain," from peine, and from Middle English peine (n.); see pain (n.). Transitive meaning "cause pain; inflict pain" is from late 14c. That of "to cause sorrow, grief, or unhappiness" also is from late 14c. In Middle English also "to punish for an offense or fault; to torture, to torment." Related: Pained; paining.

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miser (n.)

1540s, "miserable person, wretch," from Latin miser (adj.) "unhappy, wretched, pitiable, in distress," a word for which "no acceptable PIE pedigree has been found" [de Vaan]. The oldest English sense now is obsolete; the main modern meaning of "money-hoarding person" ("one who in wealth conducts himself as one afflicted with poverty" - Century Dictionary) is recorded by 1560s, from the presumed unhappiness of such people. The older sense is preserved in miserable, misery, etc.

Besides general wretchedness, the Latin word connoted also "intense erotic love" (compare slang got it bad "deeply infatuated") and hence was a favorite word of Catullus. In Greek a miser was kyminopristes, literally "a cumin seed splitter." In Modern Greek, he might be called hekentabelones, literally "one who has sixty needles." The German word, filz, literally "felt," preserves the image of the felt slippers which the miser often wore in caricatures. Lettish mantrausis "miser" is literally "money-raker."

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