Happy

Having a feeling arising from a consciousness of well-being or of enjoyment; enjoying good of any kind, such as comfort, peace, or tranquillity; blissful, contented, joyous.
Experiencing the effect of favourable fortune; favored by fortune or luck; fortunate, lucky, propitious.
Content, willing, satisfied (with or to do something); having no objection (to something).
(Of acts, speech, etc.) Appropriate, apt, felicitous.
(in combination) Favoring or inclined to use.

slaphappy, trigger-happy

(rare, of people, often followed by "at" or "in") Dexterous, ready, skilful.
Implying 'May you have a happy ~' or similar; used in phrases to wish someone happiness or good fortune at the time of a festival, celebration, or other event or activity.

Usage notes

(contented, joyous): Said of people, hours, times, thoughts, etc.
(fortunate, lucky): Said of efforts, expedients, omens, ventures, etc.

Synonyms

(contented, joyous): cheerful, content, delighted, elated, exultant, glad, joyful, jubilant, merry, orgasmic
(fortunate, lucky): fortunate, lucky, propitious

Antonyms

(contented, joyous): blue, depressed, down, miserable, moody, morose, sad, unhappy
(fortunate, lucky): unfortunate, unlucky, unpropitious
(content, satisfied): disenchanted, dissatisfied
(appropriate, apt): inappropriate, inapt, unfelicitous