'applanate' originates from French, specifically the verb 'aplaner', where 'a-' (from Latin 'ad-') meant 'to/toward' and 'plan' (from Latin 'planus') meant 'flat'.

'applanate' changed from French 'aplaner' and Neo-Latin/Scientific Latin forms such as 'applanatus' and was taken into English usage in technical contexts (especially anatomy and ophthalmology) as 'applanate'.

Initially it meant 'to make flat' in a general sense; over time it retained that core meaning but acquired a specialized sense in medicine (especially ophthalmology) meaning 'to flatten the cornea for tonometry'.