*skoto-

Proto-Indo-European root meaning "dark, shade." 

It forms all or part of: nightshade; scotoma; shade; shadow; shady.

It is the hypothetical source of/evidence for its existence is provided by: Greek skotos "darkness, gloom;" Albanian kot "darkness;" Old Irish scath, Old Welsh scod, Breton squeut "darkness," Gaelic sgath "shade, shadow, shelter;" Old English scead "partial darkness," sceadu "shade, shadow, darkness," Dutch schaduw, German Schatten, Gothic skadus "shadow."