Where does “многотысячный” come from?

многотысячный (Russian) comes from Russian ты́сяча, from Old East Slavic тысяча, from Proto-Slavic tỳsęti, from Proto-Balto-Slavic *tū́ˀsantis, from Proto-Indo-European tuHsont-, from Proto-Indo-European tewh₂- — to swell; to crowd; to be strong.

многотысячный (Russian): of many thousands

Definitions

of many thousands

Ancestry of “многотысячный”, step by step

многотысячный traces back through two separate lines of ancestry.

via Russian ты́сяча

Step	Language	Word	Meaning
1	Russian	ты́сяча	thousand
2	Old East Slavic	тысяча	—
3	Proto-Slavic	tỳsęti	—
4	Proto-Balto-Slavic	*tū́ˀsantis	thousand
5	Proto-Indo-European	tuHsont-	thousand
6	Proto-Indo-European	tewh₂-	to swell; to crowd; to be strong

via Russian мно́го

Step	Language	Word	Meaning
1	Russian	мно́го	many; much; multi-, multiple, many
2	Proto-Slavic	mъnogъ	many
3	Proto-Balto-Slavic	managas	many
4	Proto-Indo-European	monogʰos	—
5	Proto-Indo-European	mengʰ-	—

Every word from Proto-Indo-European tewh₂- →Every word from Proto-Indo-European tuHsont- →Every word from Proto-Balto-Slavic *tū́ˀsantis →