'infrequently-observed' originates from the combination of 'infrequent' and 'observe', where 'infrequent' means 'not occurring often' and 'observe' means 'to see or notice'.

'Infrequent' comes from the Latin word 'infrequens', and 'observe' comes from the Latin word 'observare'.

Initially, 'infrequent' meant 'not crowded' and 'observe' meant 'to attend to', but over time they evolved into their current meanings of 'not occurring often' and 'to see or notice'.