'occasionally-seen' originates from the combination of 'occasionally,' which comes from Latin 'occasio,' meaning 'a happening or occurrence,' and 'seen,' the past participle of 'see,' from Old English 'seon,' meaning 'to perceive with the eyes.'

'occasionally' evolved from the Latin 'occasio' through Old French 'occasion' and Middle English 'occasioun,' while 'seen' is the past participle form of 'see,' which has remained largely unchanged from Old English 'seon.'

Initially, 'occasionally' meant 'a happening or occurrence,' and 'seen' meant 'perceived with the eyes.' Together, they convey the idea of something perceived from time to time.