This is the 81st most frequent Portuguese word.
rio
River.
In this sentence, 'rio' refers to a natural stream of water that flows into seas, lakes, or other rivers, commonly translated as 'river' in English.
Eu gosto de caminhar ao longo do rio.
I like to walk along the river.
Here, 'Rio' is part of the proper noun 'Rio de Janeiro,' which is the name of a famous city in Brazil. It literally means 'River of January.'
O Rio de Janeiro é uma cidade maravilhosa.
Rio de Janeiro is a marvelous city.
In this case, the word 'riu' (different spelling) is the past tense of the verb 'rir', which means 'to laugh.' Although it shares its pronunciation with 'rio,' it serves a different function as a verb.