Where does “saaristolaiva” come from?

saaristolaiva (Finnish) comes from Finnish saaristo, from Finnish sääri, from Finnish -lä, from Finnish -as, from Proto-Finnic -s, from Proto-Finno-Ugric -s.

Ancestry of “saaristolaiva”, step by step

saaristolaiva traces back through two separate lines of ancestry.

via Finnish saaristo

Step	Language	Word	Meaning
1	Finnish	saaristo	archipelago
2	Finnish	sääri	shank, shin; cannon; used to refer to legs from...
3	Finnish	-lä	Front vowel variant of -la
4	Finnish	-as	Forms some adjectives; Forms some nouns
5	Proto-Finnic	-s	Forms nouns
6	Proto-Finno-Ugric	-s	—

via Finnish laiva

Step	Language	Word	Meaning
1	Finnish	laiva	ship; nave
2	Proto-Finnic	laiva	ship
3	Proto-Finnic	lawja	—
4	Proto-Germanic	flawją	ship, vessel
5	Proto-Indo-European	plew-	to fly, flow, run

Every word from Proto-Finno-Ugric -s →Every word from Finnish -lä →Every word from Finnish sääri →