'assertorical' originates from Latin, specifically the Late Latin adjective 'assertorius' (related to 'asserere'), where the root 'asser-' is connected to 'asserere' meaning 'to affirm' or 'to assert.'

'assertorius' passed into scholarly and philosophical English as 'assertoric' (used since the 17th–18th centuries) and later produced the extended adjective form 'assertorical' in English usage to mean 'relating to assertion.'

Initially it meant 'pertaining to affirmation or declaration,' and over time it has kept that central sense of 'relating to or characterized by assertion,' though it is now a rare or formal term.