Lillian B. Lawler, "A 'Mortar' Dance," Classical Journal
43.1 (Oct. 1947) 34:
Among the less noble forms of the Greek dance is one called variously igde, igdis, or igdisma. Pollux says in one passage (x, 103) that it is a schema, or figure; in another (iv, 101), that it is a "lascivious form of dance." Athenaeus (xiv, 629F) lists it among "funny" dances—geloiai orcheseis. Pollux (iv, 101) adds to his statement the fact that it involves rotation of the hips. Both Athenaeus and Pollux couple it with such lewd dances as the maktrismos and the apokinos. Antiphanes (see Pollux x, 103) implies that it was performed to the music of the flute. The author of the Etymologicum Magnum (pp. 464, 49-52) explains igde as "a mortar, in which we mix seasonings," and adds, "...and there is also a form of dance, igdismata, in which they used to rotate the hips in the manner of a pestle." Suidas defines igde as "a mortar," and igdisma as lygisma, that is, "writhing, twisting." Hesychius explains igdis as "mortar." In addition, he has an obscure gloss, igden:arsen, which has been emended to igden:orchesin—"a dance."
It is interesting that etymologically the names applied to this dance do not denote a pestle, as we might expect, but rather a mortar. The noun igdisma goes back to a hypothetical *igdizo, "grind, pound," which Boisacq (s.v. igdis) and Walde Hoffmann (s.v. ico) connect with Latin ico, "beat, strike." A mortar, of course, is a vessel in which something is ground, or beaten, or both.
From the names given to the dance, I believe that it must have included both a rotation of the hips, the movement which reminded the Greeks of the stirring of a pestle, and also an occasional sharp jerk, suggestive of pounding. This would differentiate it from other dances and schemata which involved similar hip movements for instance, the maktrismos, apokinos, aposeisis, rhiknousthai, etc. It was certainly a lewd performance, and was not, as some modern students of the dance have stated naively, a "folk dance" based on the "work rhythms" of pounding food in a mortar.
Oddly enough, we have an exact parallel both to the dance and to its name, in the modern theater. On the burlesque stage, rotations of the hips, I am told, are called "grinds," and sudden jerks of the body are known technically as "bumps"! Rhythmical "grinds" and "bumps," I am informed reliably, make up the typical dance of that estimable branch of our American theater. The ancient "mortar dance," be it said, was probably of about the same social standing as its modern counterpart!