The Collaborative International Dictionary
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
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.)).
pre. (context anatomy English) sphenoid bone