What is the meaning of Nił-?

Marks an reciprocal possessor; each other's

Marks an reciprocal object of a postposition

Marks a reciprocal direct object of a verb; (to, at, with) each other

In concert with other prefixes, carries several adverbial meanings when prefixed to a verb:

1. With cʼa-: opening

   With cʼa-: opening

   With dzi-: dividing, splitting in two

   With ke-: turning over

   With kʼe-: zigzaging back and forth

   With na-: making a round trip

   With ta-: mixing, combining

   together

   Marks a verb as reciprocal, meaning that two or more agents act upon one another

   Source: wiktionary.org