IPA: /əˈkeɪʒənl/
KK: /əˈkeɪʒənl/
Something that happens from time to time but not regularly; infrequent or occasional events or actions.
We go to the beach for an occasional picnic during the summer.
Occasional is formed from "occasion" (from Latin "occasio", meaning a happening or event) and the suffix "-al" (meaning pertaining to). The word "occasional" refers to something that pertains to or occurs at certain events or times, rather than regularly.
Think of an 'event' ('occasion') that happens 'pertaining to' certain times — that's why occasional means something that happens from time to time.