c. 1600, "cut in pieces," from Latin dissectus, past participle of dissecare"cut in pieces," from dis- "apart" (see dis-) + secare "to cut" (from PIE root *sek- "to cut"). Or perhaps a back-formation from dissection. Specifically as "separate the distinct parts of an animal or plant for the purpose of studying its organization and functions or its morbid affections" from 1610s. Transferred sense of "examine part by part or point by point" is from 1630s. Related: Dissected; dissecting.