An Etymological Dictionary of Astronomy and Astrophysics

1. To cut apart (an animal body, plant, etc.) to examine the structure, relation of parts, or the like.
   

2. To examine minutely part by part; analyze: to dissect an idea (Dictionary.com).

Etymology (EN): L. dissectus, p.p. of dissecare “to cut to pieces,” from
dissecare “cut in pieces,” from → dis- “apart” + secare “to cut,” → section.

Etymology (PE): Vâsekanjidan, from vâ- “apart,” → dis-, + sekanjidan “to cut to pices,” cognate with šekastan “to break,” → section.