IPA: /θiˈɛstɪkəl/
KK: /θiˈɛstɪkəl/
Relating to the belief in the existence of a god or gods.
The philosophical debate often includes theistical arguments about the nature of divinity.
The word 'theistical' is formed from 'theo-' (from Greek 'theos', meaning god) and '-ical' (meaning pertaining to or relating to). Therefore, 'theistical' refers to something that is related to or characteristic of God or deities.
Think of 'theo-' meaning god, and '-ical' meaning pertaining to, which helps you remember that 'theistical' relates to matters concerning God.