"tool for digging," Old English spadu, from Proto-Germanic *spadon (cf. Old Frisian spada, Middle Dutch spade, Old Saxon spado, Middle Low German spade, German Spaten), from PIE *spe- "long, flat piece of wood" (cf. Greek spathe "wooden blade, paddle," Old English spon "chip of wood, splinter," Old Norse spann "shingle, chip").
To call a spade a spade "use blunt language, call things by right names" (1540s) translates a Greek proverb (known to Lucian), ten skaphen skaphen legein "to call a bowl a bowl," but Erasmus mistook Greek skaphe "trough, bowl" for a derivative of the stem of skaptein "to dig," and the mistake has stuck.
