1. to reduce one's own status, importance, or dignity; to lower oneself in esteem or reputation
He refused to diminish himself by accepting their insulting offer.
Ele recusou-se a diminuir-se aceitando sua oferta insultuosa.
2. to underestimate or undervalue oneself
She tends to diminish herself when speaking about her accomplishments.
Ela tende a diminuir-se quando fala sobre suas realizações.