Formally -ise- + -taa, i.e. extracted from verbs originally formed by the suffix -taa from adjectives ending in -inen : -ise-. This reanalysis has likely been further supported by verbs such as altistaa, kaunistaa, tiivistää, valmistaa, based on adjectives of loan origin which show -is even in the nominative.
-istaa (front vowel harmony variant -istää)
- Forms verbs meaning "to make (into)", predominantly from adjectives; -ize/-ise
- Occasionally used for other purposes, either as to apply a tool onto.
- or to equip:
After labial vowels, the -i- is frequently omitted: see -staa.