This is the 704th most frequent Portuguese word.
mal
"Mal" means "evil," "bad," or "wrong" in English.
In this sentence, 'mal' is used as an adjective meaning 'ill' or 'unwell'.
Ele se sentiu mal depois de comer algo estragado.
He felt ill after eating something spoiled.
Here, 'mal' is used as an adjective to describe moral characteristics, meaning 'bad' in opposition to 'good'.
Sei que ele é jovem, mas isso não significa que ele seja mal.
I know he is young, but that doesn't mean he is bad.
In this sentence, 'mal' is part of a compound noun ('mal-entendido'), indicating a concept of 'mis-' or 'ill misunderstanding'.