Where does “erojaistilaisuus” come from?

erojaistilaisuus (Finnish) comes from Finnish tilaisuus, from Finnish tila, from Finnish -inen, from Finnish -uus, from Proto-Finnic -uc — -ness, -hood.

Ancestry of “erojaistilaisuus”, step by step

erojaistilaisuus traces back through two separate lines of ancestry.

via Finnish tilaisuus

Step	Language	Word	Meaning
1	Finnish	tilaisuus	occasion; opportunity, chance
2	Finnish	tila	state; condition; Short for maatila
3	Finnish	-inen	-like, -ous, -y; -en; Creates adjectives from...
4	Finnish	-uus	Forms nouns from adjectives, expressing a quality
5	Proto-Finnic	-uc	-ness, -hood

via Finnish erojaiset

Step	Language	Word	Meaning
1	Finnish	erojaiset	sendoff farewell party
2	Finnish	ero	difference, distinction; Short for avioero;...
3	Finnish	-o	Forms result or action nouns from verbs; Forms...
4	Proto-Finnic	-o	Forms action/result nouns from verbs
5	Proto-Uralic	-w	—

Every word from Proto-Finnic -uc →Every word from Finnish -inen →Every word from Finnish -uus →