1. To lose strength, energy, or determination towards the end of a task, race, or effort
The runner weakened at the finish and lost the race.
O corredor perdeu força no final e perdeu a corrida.
2. To become less effective or convincing in the final stages of an argument or presentation
His argument weakened at the finish, leaving the jury unconvinced.
Seu argumento perdeu força no final, deixando o júri inconvincido.