"one who gives his opinion in cases of law," c. 1600, from Latin iurisconsultus, originally two words, genitive of ius "law" (see jurist) + present participle of consultare "consult, take the advice of" (see consultation).
mid-15c., "one who practices law;" 1620s, "a legal writer, one who professes the science of the law," from French juriste (14c.), from Medieval Latin iurista "jurist," from Latin ius (genitive iuris) "a right," especially "legal right or authority, law," also "place where justice is administered, court of justice," from Old Latin ious, perhaps literally "sacred formula," a word peculiar to Latin (not general Italic) that originated in the religious cults, from PIE root *yewes- "law" (compare Latin iurare "to pronounce a ritual formula," Vedic yos "health," Avestan yaoz-da- "make ritually pure," Irish huisse "just"). Related: Juristic. The more mundane Latin law-word lex meant specific laws as opposed to the body of laws.
The Germanic root represented by Old English æ "custom, law," Old High German ewa, German Ehe "marriage," sometimes is associated with this group, or it is traced to PIE *ei- "to go."
early 15c., "a meeting of persons to consult together;" 1540s, "act of consulting," from Latin consultationem (nominative consultatio) "a mature deliberation, consideration," noun of action from past-participle stem of consultare "to consult, ask counsel of; reflect, consider maturely," frequentative of consulere "to deliberate, consider," originally probably "to call together," as in consulere senatum "to gather the senate" (to ask for advice), from assimilated form of com "with, together" (see con-) + *selere "take, gather," for a total sense of "gather (the Senate) together," from PIE *selho- "to take, seize."
De Vaan writes: "Since consuleredoes not look like a derivative of consul (we would rather expect consulare), it appears that the verb was original and meant 'to get together, deliberate'."