Learn Portuguese (Portugal): O aluno tem uma multa, mas o bibliotecário não lha mostra. - The student has a fine, but the librarian doesn't show it to him.

lha is a contraction of two pronouns: lhe (meaning "to him") and a (meaning "it", referring to a feminine noun). Together, they mean "it to him". This double pronoun saves us from having to repeat the words for both the student and the fine!

If the student (o aluno) is masculine, why does lha end with an "a"?

The ending of lha matches the thing being shown, not the person receiving it. Here, the librarian is showing a fine (a multa), which is a feminine noun. The lh- part of the word comes from lhe, which means "to him" and is used for both masculine and feminine recipients.

Why is lha placed before the verb (mostra) instead of after it?

Normally, in European Portuguese, object pronouns attach to the end of the verb with a hyphen. However, the negative word não acts like a magnet and pulls the pronoun to the front of the verb. Because of the não, we must say não lha mostra instead of não mostra-lha.

Would the pronoun change if the librarian was a woman (a bibliotecária)?