What is the meaning of -mu-?

a shortened allomorph of the monoclonal antibody affix -mul-, used before the affixes -xi- and -zu- for ease of pronunciation

Class 1 object concord.

1. 3rd person singular direct object, him/her

3rd person singular direct object, him/her

3rd person singular object concord.

her, him; 3rd person singular (m class_(I)) object concord used before /u/ and /w/

Class 1 object concord.

Source: wiktionary.org