ja, m. the chief-defendant or prosecutor in an Icel. lawsuit in the time of the Commonwealth. It seems to have meant originally head, chieftain, princeps. A standing word in the Grágás and the Sagas. As to the form, the older one is that which preserves the j in the terminations, gen. dat. acc. aðilja, plur. -jar, acc. -ja, dat. -jum. The Grágás constantly employs this form. The Njála and some of the Sagas drop the j and write aðila etc. In the Grágás aðilja seems to occur as an indecl. word—at least four times in the Kb.—used as nom. pl.: but as -ar in old MSS. is frequently marked by a single ‘a’ with a little stroke (a-), this may be a misinterpretation. The indeclinable form occurs in the Kb. (Þ. Þ.) 25 and 109 (only preserved in the Kb.); Kb. 147, 170 has aðilja, where the Sb. has in both passages aðiljar: cp. however guðsifja and -bræðra. There is a distinction between a sóknar-aðili or sakar-aðili, prosecutor, and a varnar-aðili, defendant. Either with gen. or prep. at, varnar-a., sóknar-a., sakar-a.; or inversely, a. sakar, a. varnar, a. frumsakar, Kb. 42, 124; a. máls, 126; a. vígsakar, in a case of manslaughter, 167; or vígsakar a. (often); a. fésakar, in a lawsuit about compensation, 123; a. legorðssakar, case of legorð, 194: with at, varnir þær er hann er aðili at, 175; aðili at legorðs sekt, App. iv. 46, Grág. Kb. 15, 211 ; cp. also § 58, p. 103: hann er aðili at sök, bæði sækjandi ok seljandi, chief-plaintiff, either for carrying it on himself or by a delegate, Kb. 208. In the case of a delegate being the aðili, the challenge of jurors and judges on account of relationship was to be made in respect to the chief aðili, not the delegate, Kb. 127.