extend: Latin extendo = extend or stretch out, hence, extension = extended or straightened; the position opposite to the flexed or bent.
external: adjective, Latin externus = outward, hence, further from the inside.
extraperitoneal: adjective, Latin extra = outside, Greek peri = around and teinein = stretched, hence outside the serous membrane stretched around the inside of the abdominal wall and around the viscera.
extrapyramidal: Latin extra = outside, and pyramidal (q.v.), hence descending nerve tracts that do not traverse the pyramids of the medulla.
extrinsic: Latin extrinsecus = from without, hence (usually) a muscle (usually) originating outside the part on which it acts.