1. denies or contradicts (a statement or claim); says something is not true
Usage: third-person singular present tense of 'gainsay'; formal or literary
2. speaks against or opposes; argues against
Usage: third-person singular present tense of 'gainsay'; formal or literary

Examples

• No one gainsays the importance of education in modern society.
• The evidence gainsays his earlier claims about the accident.
• She gainsays every proposal he makes at the meeting.
• The facts gainsay the official explanation.
• He gainsays the traditional interpretation of the text.
• The witness gainsays the defendant's testimony.
• Few would gainsay that climate change is a serious issue.