Where does “ծերունի” come from?

ծերունի (Armenian) comes from Old Armenian ծերունի, from Old Armenian -ունի, from Old Armenian -ուն, from Proto-Indo-European -o-mno-, from Proto-Indo-European -o-meno- — adverbial suffix of neuter gender.

ծերունի (Armenian): old man; aged; old age; senile

Definitions

old man; aged; old age; senile

Ancestry of “ծերունի”, step by step

Step	Language	Word	Meaning
1	Old Armenian	ծերունի	old man or woman; aged, old; senile
2	Old Armenian	-ունի	forming adjectives; denoting a member of a...
3	Old Armenian	-ուն	forming adjectives from verbs and rarely from...
4	Proto-Indo-European	-o-mno-	—
5	Proto-Indo-European	-o-meno-	adverbial suffix of neuter gender

Every word from Proto-Indo-European -o-meno- →Every word from Old Armenian -ուն →Every word from Old Armenian -ունի →