spade n.1

"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-(source also of Greek spathē "wooden blade, paddle"), which as a suffixed form has been grouped under a root *speh-, "with several extensions, denoting quite different implements" (Boutkan) but basically indicating "long, flat piece of wood" (source also of 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 skaphē "trough, bowl" for a derivative of the stem of skaptein "to dig," and the mistake has stuck [see OED].

black figure on playing cards," 1590s, probably from Italian spade, plural of spada "the ace of spades," literally "sword, spade," from Latin spatha "broad, flat weapon or tool," from Greek spathe "broad blade" (see spade (n.1)). Phrase in spades "in abundance" first recorded 1929 (Damon Runyon), probably from bridge, where spades are the highest-ranking suit.

The invitations to the musicale came sliding in by pairs and threes and spade flushes. [O.Henry, "Cabbages & Kings," 1904]

Derogatory meaning "black person" is 1928, from the color of the playing card symbol.