pizca

a little bit, ounce, iota, smidgeon, modicum, trace, lick; pinch, dash (e.g., a pinch of salt, a dash of vanilla extract)

“Pero no existe ni una pizca de evidencia en absoluto.” — There isn't even a shred of evidence whatsoever.

From pizco, from pizcar, itself of onomatopoeic origin.