This is the 434th most frequent Portuguese word.
mínimo
"Minimum; least or smallest amount or degree."
In this sentence, 'mínimo' is used as an adjective to describe 'preço', indicating the least or smallest value for the price.
O preço mínimo deste produto é 5 reais.
The minimum price of this product is 5 reais.
Here, 'mínimo' functions as an adjective modifying 'sinal', meaning the least or smallest indication.
Ao mínimo sinal de cansaço, devemos parar para descansar.
At the slightest sign of tiredness, we should stop to rest.
In this usage, 'mínimo' serves as a noun referring to the least or smallest effort or action possible.