It forms all or part of: abscissa; conscience; conscious; ecu; escudo; escutcheon; esquire; nescience; nescient; nice; omniscience; omniscient; plebiscite; prescience; prescient; rescind; rescission; science; scienter; scilicet; sciolist; scission; schism; schist; schizo-; schizophrenia; scudo; sheath; sheathe; sheave (n.) "grooved wheel to receive a cord, pulley;" shed (v.) "cast off;" shin (n.) "fore part of the lower leg;" shingle (n.1) "thin piece of wood;" shit (v.); shive; shiver (n.1) "small piece, splinter, fragment, chip;" shoddy; shyster; skene; ski; skive (v.1) "split or cut into strips, pare off, grind away;" squire.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit chindhi, chinatti "to break, split up;" Avestan a-sista- "unsplit, unharmed," Greek skhizein "to split, cleave, part, separate;" Latin scindere "to cut, rend, tear asunder, split;" Armenian c'tim "to tear, scratch;" Lithuanian skiesti "to separate, divide;" Old Church Slavonic cediti "to strain;" Old English scitan, Old Norse skita "to defecate;" Old English sceað, Old High German sceida "sheath;" Old Irish sceid "to vomit, spit;" Welsh chwydu "to break open."
"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 skaphē "trough, bowl" for a derivative of the stem of skaptein "to dig," and the mistake has stuck [see OED].