-oi-

Finnish

Etymology

The -i- has labialized the preceding -a- (initially only for back vowels, but the suffix has been later generalized for front vowels as well).

Interfix

-oi- (front vowel harmony variant -öi-, linguistic notation -Oi-)

1. Alternative form of -i- (“plural marker”)

   kasassa - kasoissa ― in the pile - in the piles

Usage notes

• if the plural indicator is between two vowels it becomes -oj-

  kasan - kasojen ― of the pile - of the piles