-istical

Etymology
Combination of the adjective suffixes -istic (-ist + -ic) and -al.

Suffix

 * 1) Used to form adjectives meaning of or relating to corresponding nouns ending in -istic or -ist; most often redundant with respect to the latter which can also become adjectives through the addition of -ic alone, or with no change to the root noun. Hence, theist, theistic and theistical can all be used as the adjective form of theism.