Proto-Indo-European *skeh₂i- "to gleam" in the suffixed zero-grade form *skeh₂i-no- became Proto-Germanic *skīnan and English shine.
It's thought the word also meant "shadow", or maybe its sense changed to "shadow" in some cases? Anyway the Greek derivative is apparently σκιά "shadow". This combined with οὐρά "tail" to form σκίουρος "shadow-tail, i.e. squirrel". This was borrowed into Latin as sciūrus, and diminutivized to scurellius, becoming Old French esquireul, escureul (whence modern French écureuil), becoming Anglo-French esquirel, borrowed into English as squirrel.
Possibly there was a suffixed form *skeh₂i-nto- which became Latin scintillāre "to sparkle, glitter". This became *stincillāre by metathesis, becoming Old French estinceler "to sparke, to sparkle as fire; to twinkle as a starre or Dyamond; to set thicke with sparkles" (Cotgrave). The past participle estincelé "sparkled, sparked, also powdered or set with sparkles" found its way into English as tinsel, tincel.