1
- a particular time or instance of an event时刻; 场合：
on one occasion I stayed up until two in the morning.
有一次我直到凌晨2点才去睡觉。
1.1
- a special or noteworthy event, ceremony, or celebration重大场合,仪式,庆典：
she was presented with a gold watch to mark the occasion
为了纪念那个重大场合她被赠与一块金表
mass noun Sunday lunch has a suitable sense of occasion about it.周日午餐给人一种恰如其分的重大场合的感觉。
1.2
- a suitable or opportune time for doing something适当时机：
by-elections are traditionally an occasion for registering protest votes.
补缺选举向来都是记反对票的适当时机。
2
- mass noun formal reason; cause理由; 原因：
with infinitive it's the first time that I've had occasion to complain.这是我第一次有理由抱怨。
with obj.
- formal cause (something)造成, 导致, 引起：
something vital must have occasioned this visit
肯定有什么重大的事导致了这次访问
with two objs his death occasioned her much grief.他的死使她十分悲痛。
短语
on occasion（或occasions）
- occasionally; from time to time有时; 偶尔：
on occasion, the state was asked to intervene.
有时政府会被要求进行干预。
rise to the occasion
- perform better than usual in response to a special situation or event在特殊场合超常发挥, 在特殊场合应付裕如。
take occasion
- archaic make use of an opportunity to do something〈古〉抓住时机。
词源
late Middle English: from Latin occasio（n-） 'juncture, reason', from occidere 'go down, set', from ob- 'towards' + cadere 'to fall'.