The Collaborative International Dictionary
Spheno-
Spheno- \Sphe"no-\ A combining form used in anatomy to indicate connection with, or relation to, the sphenoid bone; as in sphenomaxillary, sphenopalatine.
Douglas Harper's Etymology Dictionary
spheno-
before vowels sphen-, word-forming element meaning "wedge," from comb. form of Greek sphen "a wedge," probably cognate with Old Norse spann "splinter," Old English spon "chip of wood" (see spoon (n.)).
Wiktionary
spheno-
pre. (context anatomy English) sphenoid bone