تضاحك

and ↓ تضحّك [are both mentioned in the K and TA as though synonym with each other and with ضَحِكَ: and according to the KL, the former signifies He laughed: but according to the TK, the latter signifies he manifested laughing: or] the former is synonym with ↓ استضحك [apparently as meaning he affected to laugh, or laughing: or, more exactly, agreeably with analogy, like the contr. تَبَاكَى and اِسْتَبْكَى, the former signifies thus; and the latter, he desired to laugh]. (S.)

And you say also, هُمْ يَتَضَاحَكُونَ [meaning They laugh together, one with another]. (K.)