دِرْسٌ

The relic, trace, or mark, of a thing that becomes effaced, erased, rased, or obliterated. (M.)

(tropical:) An old and worn-out garment, or piece of cloth; (S, M, A, K;) [apparently an epithet used as a subst.;] as also ↓ دَرْسٌ (M) and ↓ دَرِيسٌ; (S, M, A, K;) ↓ which last also signifies an old and worn-out carpet; (A;) ↓ and as an epithet, signifying old and worn-out, is applied to a coat of mail, (M, TA,) and to a sword, and to a مِغْفَر [&c.]: (TA:) plural [of the first] أَدْرَاسٌ, (M, K,) [a plural of pauc.,] and [of the same or of either of the others] دِرْسَانٌ. (S, M, K.)

[Hence, or, as IF says, from الحَيْض,] أَبُو أَدْرَاسٍ [in some copies of the K أُمُّ أَدْرَاسٍ] (tropical:) The pudendum muliebre. (S, O, K.)