What is the meaning of -un?

of

Suffix denoting present tense.

Used to derive nouns from class 2 weak verbs.

Suffix variant for the illative singular: see -Vn.

Forms nouns from verbs (generally class 4 weak verbs) denoting the action or state described by the verb

forms masculine nouns

An epenthetic variant of -n (the suffixation of the second-person singular possession), agglutinated after a syllable which ends in a consonant and contains a rounded back vowel

Variant of -nun (suffix forming genitive), agglutinated after a syllable which ends in a consonant and contains a rounded back vowel

Source: wiktionary.org