ثلث

ثَلَاثُونَ ثلاثون , [also written ثَلٰثُونَ,] the noun of number, [meaning Thirty, and also thirtieth, ] is not considered as a multiple of ثَلَاثَةٌ, but as a multiple of عَشَرَةٌ; and therefore, if you name a man ثَلَاثُونَ, you do not make the dim. to be ثَلِيِّثُون, but [you assimilate the noun from which it is formed to a pl. with و and ن from عَشَرَةٌ, or to عِشْرُونَ, and say] ↓ ثُلَيْثُونَ. (Sb, M.)