Occasion n. : A falling out, happening, or coming to pass; hence, that which falls out or happens; occurrence; incident.

Occasion n. : A favorable opportunity; a convenient or timely chance; convenience.

Occasion n. : An occurrence or condition of affairs which brings with it some unlooked-for event; that which incidentally brings to pass an event, without being its efficient cause or sufficient reason; accidental or incidental cause.

Occasion n. : Need; exigency; requirement; necessity; as, I have no occasion for firearms.

Occasion n. : A reason or excuse; a motive; a persuasion.

Occasion v. t. : To give occasion to; to cause; to produce; to induce; as, to occasion anxiety.

Example:
What shirt to wear for a special Occasion?

Taxonomy
Merriam-Webster Online Dictionary, Dictionary, circumstance, webster, Anglo-French, Latin, Word Games, Webster Online Dictionary with audio pronunciations, Middle English, state of affairs, glossary, language, ESL, zh, Etymology, occasio, occidere, fall down.

Defination from the web:
occasion from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... 1 : a favorable opportunity or circumstance <did not have occasion to talk with them> ...