Desentristecer is a fascinating word because it's formed by adding the prefix 'des-' (meaning 'un-' or 'undo') to 'entristecer' (to sadden). It literally means 'to unsadden' or 'to make happy again'.
In the song, the singer says, "Para desentristecer, leãozinho, o meu coração tão só" (To unsadden, little lion, my so lonely heart). It beautifully conveys the idea that the 'leãozinho' (little lion) has the power to lift their spirits and bring joy back to a solitary heart.
"O Leãozinho" was written by Caetano Veloso, and Ana Vilela's version keeps it stripped down to acoustic guitar and voice. She sings to someone she calls her "leãozinho" — her little lion — watching him walk through the light: "Caminhando sob o sol" ("Walking under the sun"). The song stays close to that one image of sun and skin instead of reaching for a bigger metaphor.
By the second verse she's naming the parts of him she loves — "Tua pele, tua luz, tua juba" ("Your skin, your light, your mane") — and admitting she wants to be near him in it too: "De estar perto de você e entrar no mar" ("Being close to you and going into the sea"). The closing line, "Gosto muito de você, leãozinho" ("I really like you, little lion"), repeats like a held breath rather than building toward anything bigger, and Vilela's quiet arrangement leaves enough space around it that the repetition reads as devotion, not filler.