This is the 4045th most frequent Portuguese word.
mônica
"Mônica" is a proper noun, typically a female given name, equivalent to "Monica" in English.
The word 'Mônica' is used as a proper noun to name an individual and is the subject of the sentence.
Mônica é uma pessoa muito gentil.
Mônica is a very kind person.
Here, 'Mônica' is used as a proper noun in a possessive structure ('da Mônica') to denote ownership of the mentioned item (the t-shirt).
A camiseta da Mônica está lavada.
Mônica's t-shirt is washed.
In this sentence, 'Mônica' is again a proper noun in a possessive structure ('da Mônica'), this time indicating the thematic association with the comics.