'apotelesmatical' originates from Greek, specifically the word 'apotelesma' meaning 'result, effect', later formed into Medieval/Neo-Latin 'apotelesmaticus' and Englishized as 'apotelesmatic'/'apotelesmatical'.

'apotelesma' (Greek) passed into Late Latin/Medieval Latin as 'apotelesmat-' or 'apotelesmaticus', and then into English as 'apotelesmatic' with the adjectival variant 'apotelesmatical'.

Initially it referred broadly to a 'result' or that which produces an outcome; over time it came to be used especially of astrological influences and, more generally, of something possessing operative effect.