This is the 6980th most frequent Portuguese word.
invisível
Invisible.
Here, 'invisível' is used literally to mean 'unable to be seen', describing the action of becoming hidden from sight.
O manto mágico tornou o guerreiro invisível aos seus inimigos.
The magical cloak made the warrior invisible to his enemies.
In this case, 'invisível' is used metaphorically to describe a feeling of being unnoticed or ignored in a social setting.
Ela se sentia invisível na multidão, como se ninguém reparasse nela.
She felt invisible in the crowd, as if no one noticed her.
Here, 'invisível' is used to refer to something imperceptible to the human senses yet still present and effectual.