Where does “Янтарски” come from?

Янтарски (Bulgarian) comes from Turkish yan, from Ottoman Turkish یان, from Proto-Turkic yān — side.

Ancestry of “Янтарски”, step by step

Янтарски traces back through two separate lines of ancestry.

via Turkish yan

StepLanguageWordMeaning
1Turkishyanside; second-person singular imperative of yanmak
2Ottoman Turkishیانside
3Proto-Turkicyānside

via Russian янта́рь

StepLanguageWordMeaning
1Russianянта́рьamber (fossil resin)
2Lithuaniangintàrasamber (fossil resin)
Every word from Proto-Turkic yān →Every word from Ottoman Turkish یان →Every word from Turkish yan →