ثأب1 ثُئِبَ, ('Eyn, T, M, K,) like عُنِىBَ, (K,) and ثَئِبَ, (IKoot, L, and so in a copy of the A,) inf. n. ثَأْبٌ, (K,) or ثَأَبٌ, (M,) He became relaxed and sluggish; said of a man: (A:) or he became affected with sluggishness and languor; (M;) as also ↓ تثآءب: (M, A:) or he became affected with sluggishness and languor like the languor of drowsiness; as also ↓ تثآءب and ↓ تثأّب; (K;) which  last is approved by IDrd and Thábit Es-Sara- kustee, who disallow ↓ تثآءب, though this is the form commonly known and approved, and is the most chaste form: (TA:) or he became affected with languor like the heaviness of drowsiness, in consequence of something that he had eaten or drunk, without becoming insensible; (T;) as also ↓ تثآءب: (L:) or ↓ this last signifies he yawned, or opened his mouth, (Mgh, Msb,) by reason, (Mgh,) or on the occasion, (Msb,) of languor (Mgh, Msb,) like the heaviness of drowsiness; (Mgh;) or he yawned, or opened his mouth, and stretched himself, on being affected by sluggishness or drowsiness or anxiety; (MF, TA, on the authority of IDrst;) or he yawned, or opened his mouth, and emitted wind from his stomach, by reason of some affection thereof: (TA on the authority of EtTedmuree:) التَّثَاؤُبُ is from الثُّؤَبَآءُ; (Az, T, S, Mgh;) and is on the occasion of one's stretching  himself, and being languid: (Lth, T:) one should not say تَثَاوَبَ; (Az, T, S, O, Mgh;) [for] this is vulgar. (Msb.) Hence, أَحَدُكُمْ فَلْيُغَطِّ ↓ إِذَا تَثَأَءَبَ فَاهُ [When any one of you yawns, he should cover his mouth with the back of his left hand; for it is believed that the devil leaps into the uncovered yawning mouth]. (Mgh.) 5 تَثَاَّ^َ see 1.6 تَثَاَّ^َ see 1, in six places.ثُؤَبَآءُ, (T, S, M, K, &c.,) as also ثُؤْبَآء, accord. to Ibn-Mis-hal, but this is strange, (TA,) is a subst. derived from التَّثَاؤُبُ, like مُطُوَآءُ from التَّمَطِّى; (T;) or from ثَئِبَ; and means A state of relaxation and sluggishness: (A:) or sluggishness and languor (M, K) like the languor of drowsiness: (K:) or languor like the heaviness of drowsiness, in consequence of something that one has eaten or drunk, not attended by insensibility: (T, L:) or a yawning, or opening the mouth, by reason of languor like the heaviness of drowsiness: (Mgh:) or a yawning, or opening the mouth, and stretching oneself, on being affected by sluggishness or drowsiness or anxiety: (IDrst, MF, TA:) or a yawning, or opening the mouth, and emitting wind from the stomach, by reason of some affection thereof. (Et-Tedmuree, TA.) Hence the prov., أَعْدَى مِنَ الثُّؤَبَآءِ, (S, A, TA,) and [الثُّوَبَآءِ,] without ء, as some say; (MF;) or the pronunciation without ء  is vulgar, (IDrst, TA,) or erroneous; (TA;) [More catching than yawning;] for when a man yawns ( اذا تثاءب ) in the presence of others, they become affected as he is. (TA.) مَثْؤُوبٌ Affected with sluggishness and languor like the languor of drowsiness: from ثُئِبَ, q. v. (K.)