'rarely-combined' originates from the English words 'rarely' and 'combined', where 'rarely' means 'not often' and 'combined' means 'joined together'.

'rarely' and 'combined' have been used separately in English since the Middle Ages, and their combination into 'rarely-combined' is a modern usage to describe infrequent conjunctions.

Initially, 'rarely' and 'combined' were used separately, but their combination into 'rarely-combined' specifically describes infrequent pairings.