"tool for digging," Old English spadu "spade," from Proto-Germanic *spadan (source also of Old Frisian spada "a spade," Middle Dutch spade "a sword," Old Saxon spado, Middle Low German spade, German Spaten), from PIE *spe-dh-, from root *spe- (2) "long, flat piece of wood" (source also of Greek spathe "wooden blade, paddle," Old English spon "chip of wood, splinter," Old Norse spann "shingle, chip;" see spoon (n.)).

"A spade differs from a two-handed shovel chiefly in the form and thickness of the blade" [Century Dictionary]. 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 [see OED].