The term 'seldom-seen' is a compound adjective formed from 'seldom' and 'seen'. 'Seldom' originates from Old English 'seldan', meaning 'rarely', and 'seen' is the past participle of 'see', from Old English 'seon'.

The phrase 'seldom-seen' evolved from the combination of 'seldom' and 'seen', both of which have roots in Old English.

Initially, 'seldom' meant 'rarely' and 'seen' meant 'observed'. The compound 'seldom-seen' retains this meaning of being rarely observed.