O13.occasion，occasional

occasion，occasional

构词：oc（=ob-，面前）＋cas（= fall，“咔嗒”掉下）＋ion（n.）

（机会）降临在面前 n. 时机、机会；事件、场合

相关：case，chance，casual，casualty，accident，incident，coincide；cascade，catastrophe；occasionally

搭配：an occasion for / for the occasion；if the occasion arises / rise to the occasion；on this / that occasion；mark the occasion；

important / special occasion；on several / separate occasions。

occasional drinking / visit / rain 

近义：chance，opportunity，moment，point，cause；

            incident，instance，event，occurence