The Latin lacus, "reservoir, lake" is the origin, in the primitive vocabulary heritage, of the Portuguese, Spanish, and Italian lago, French lac; one of its derivatives, the Latin lacuna, "pitfall, hole", "lack, want, neglect", explains the Spanish and Italian laguna. But the Portuguese lagoa, coincidentally with the Spanish lagona and Mirandese llagona, suggests a change in suffix, already documented in a 938 document from Valencia, under the spelling lacona, and in another from 1094, in Sahagún, under the spelling lagona. The Portuguese lagoa under the spelling lagona (perhaps lagõna), is documented in the 14th century, and alternated with the other for a long time; the prosthesis is then explained by the introduction of the article, chiefly in locution (na lagoa, vindo da lagoa) (in the lake, coming from the lake), and for morphologic regularization with the derivatives of the verb alagar (to inundate) (alagadiço, alagado, alagador, alagamento, etc.) (swampish, waterlogged, flooding, overflow, etc.).
The name appears as a competitor with the names of the lagoons of Manguaba, a lagoa do sul ("the southern lagoon"), and Mundaú, a lagoa do norte ("the northern lagoon"), already in the 16th century, when settlements were founded near the Alagoa do Norte and the Alagoa do Sul, the Alagoas, with the inclusion of the rest of the lagoons in the area.
Alagoas m, f pl
- Alagoas (state in north-eastern Brazil)