Definition of occasion :
1. A falling out, happening, or coming to pass; hence, that which falls out or happens; occurrence; incident.
2. A favorable opportunity; a convenient or timely chance; convenience.
3. A reason or excuse; a motive; a persuasion.
4. 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.
5. Need; exigency; requirement; necessity; as, I have no occasion for firearms.
6. To give occasion to; to cause; to produce; to induce; as, to occasion anxiety.
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circumstance (part of speech: noun)