dissertation (n.) Look up dissertation at Dictionary.com
1610s, "discussion, debate," from Latin dissertationem (nominative dissertatio) "discourse," noun of action from past participle stem of dissertare "debate, argue, examine, harangue," frequentative of disserere "discuss, examine," from dis- "apart" (see dis-) + serere "to arrange words" (see series). Sense of "formal, written treatise" is 1650s.