Letargo translates to "lethargy" or "slumber." It's a less common word in everyday Spanish, making it stand out in the lyrics.
In "Bachata Rosa," the singer uses it poetically to describe a deep, dream-like state of love: "Un letargo de azul, un eclipse de mar." This imagery evokes a sense of being completely immersed and lost in the beauty of love, like a tranquil, blue slumber or a captivating eclipse of the sea.
"Bachata Rosa" is Juan Luis Guerra's own signature bachata, revisited here as a duet with Natalie Cole for her Spanish-language recordings. Guerra wrote and popularized the song in the late 1980s; this version keeps his voice on the track while Cole carries the melody, an American soul singer stepping into a style built in the Dominican Republic.
The lyrics turn a rose into a stand-in for the person being loved, questioning her the way you'd question a stranger: "No sé si está desnuda, o tiene un solo vestido" (I don't know if it's naked, or if it has only one dress), "Si alguna vez fue amada, o tiene amor escondido" (If it was ever loved, or if it has hidden love). The chorus switches to astronomy — "Yo soy satélite y tú eres mi sol" (I am a satellite and you are my sun) — casting the singer as a body that only shines by reflecting someone else's light.