1. to lack variety, interest, or excitement; to be tediously uniform or repetitive
The lecture was so monotonous that half the class fell asleep.
A aula foi tão monótona que metade da turma dormiu.
2. to speak or sound in a dull, unchanging tone without variation in pitch or inflection
His voice tends to be monotonous when he reads from a script.
Sua voz tende a ser monótona quando lê de um roteiro.