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bis-

word-forming element meaning "twice," from Latin bis "twice, in two ways, doubly," from Old Latin dvis, cognate with Sanskrit dvih, Avestan bish, Greek dis, Middle High German zwis "twice," from PIE *dwo- "two" (see two). Also the form of bi- used before -s-, -c-, or a vowel.

Online Etymology Dictionary, © 2010 Douglas Harper

bis- in Medicine

bis-

pref.
  1. Two; twice:bisalbuminemia.
  2. Having two identical but separated complex chemical groups in one molecule:1,4-bis(5-phenyloxazol-2-yl)-benzene.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.