sombra

shadow (a dark image projected onto a surface where light (or other radiation) is blocked by the shade of an object); shade (darkness where light, particularly sunlight, is blocked); shade, shadow (a small degree); ghost, shade, phantom; shade (a color obtained by adding black)

“sin sombra de duda” — without a shadow of a doubt

Possibly from the verb sombrar (from Vulgar Latin *subumbrāre), or more likely from Latin umbra (“shade, shadow”), possibly altered by influence from sol (“sun”) (cf. Old Spanish solombra (literally “sunshade”)) or the Latin prefix sub-. An alternative explanation for this form is a Latin construction sub illa umbra (“under that shade”).