'antisceptical' originates from English, formed by the prefix 'anti-' (from Greek 'anti' meaning 'against') + 'sceptical' (from Greek 'skeptikos' via Latin and Old French).

'sceptical' derives from Greek 'skeptikos' → Latin/Medieval forms → Old/Middle French 'sceptique' → Middle English 'sceptical'; the productive English prefix 'anti-' was attached in modern usage to create 'antisceptical'.

Initially it literally meant 'against scepticism' and, in usage, has retained that core sense of opposing or not sharing a sceptical attitude.