'tonsillar' originates from Latin, specifically the word 'tonsillae,' where 'tonsilla' meant 'tonsil.' The suffix '-ar' is used to form adjectives meaning 'pertaining to.'

'tonsilla' in Latin was adopted into medical Latin as 'tonsilla,' and the adjective form 'tonsillaris' became 'tonsillar' in modern English.

Initially, it meant 'pertaining to the tonsils,' and this meaning has remained unchanged in modern usage.