gain ‧ say /ˌɡeɪnˈseɪ/ BrE AmE verb ( past tense and past participle gainsaid /-'sed/) [transitive usually in negatives] formal
[ Date: 1300-1400 ; Origin: gain- 'against' (13-16 centuries) (from Old English gegn ) + say ]
to say that something is not true, or to disagree with someone SYN contradict :
No one dared to gainsay him.