late 14c., deliberacioun, "act of weighing and examining," from Old French deliberation, from Latin deliberationem (nominative deliberatio), noun of action from past-participle stem of deliberare "consider carefully, consult," literally "weigh well," from de, here probably "entirely" (see de-) + -liberare, altered (probably by influence of liberare "to free, liberate") from librare "to balance, make level," from libra "pair of scales, a balance" (see Libra).
Sense of "slowness in decision or action" is from early 15c. Meaning "mutual discussion and examination of the reasons for and against a measure" is from late 15c..