كأس كَأْسٌ, (ISk, S, A, Msb, K,) and كَاسٌ, with the ء suppressed, is allowable, (Msb,) and sometimes occurs, (TA,) A drinking-cup: (A, K:) or [a cup of wine; i. e.] a cup containing wine; (S, A, K;) or a cup full of wine: (Msb:) when not containing wine, it is not thus called; (IAar, S, Msb;) being in this case called قَدَحٌ: (TA:) or it has the first and the second of these significations: (TA:) or it signifies wine itself: (As, AHát, Ibn-'Abbád:) or has this signification also: (K:) and is of the fem. gender: (S, A, Msb, K:) pl. [of pauc.] أَكْؤُسٌ and [of mult.] كُؤُوسٌ and كِئَاسٌ, (S, Msb, K,) the last with ء, (TA, [but written without ء in the CK,]) and, accord. to AHn, كِيَاسٌ, without ء, which, if correct, is originally كِوَاسٌ, from كَاسٌ, with the ء changed into ا as representing و, (TA,) and كَاسَاتٌ, (K,) without ء. (TA.) It is used metaphorically in relation to every kind of disagreeable, hateful, or evil, things. Thus you say, سَقَاهُ كَأْسًا مِنَ الذُّلِّ (tropical:)  [He gave him to drink a cup of abasement]: and مِنَ الفُرْقَةِ (tropical:)  [of separation]: and مِنَ المَوْتِ (tropical:)  [of death]: and مِنَ الحُبِّ (tropical:)  [of love]. (TA.) You say also, سَقَاهُ الكَأْسَ الأَمَرَّ (tropical:)  [He gave him to drink the most bitter cup]; meaning death: (A, TA:) and كُؤُوسَ المَنَايَا (tropical:)  [The cups of death; lit., deaths]. (A.) Az. thinks that it may be derived from كَاصَ فُلَانٌ مِنَ الطَّعَامِ وَالشَّرَابِ, meaning, “ Such a one ate and drank much ”; because ص and س are interchangeable in many words on account of the nearness of their places of utterance. (TA.)