Where does “nůsek” come from?

nůsek (Czech) comes from Czech nos, from Old Czech nos, from Proto-Slavic nȍsъ, from Proto-Balto-Slavic nasús, from Proto-Indo-European néh₂s- — nose, nostril.

Ancestry of “nůsek”, step by step

Step	Language	Word	Meaning
1	Czech	nos	nose; second-person singular imperative of nosit
2	Old Czech	nos	nose
3	Proto-Slavic	nȍsъ	nose
4	Proto-Balto-Slavic	nasús	nose
5	Proto-Indo-European	néh₂s-	nose, nostril

Every word from Proto-Indo-European néh₂s- →Every word from Proto-Balto-Slavic nasús →Every word from Proto-Slavic nȍsъ →