This is the 1943rd most frequent Portuguese word.
metrô
Subway or metro (underground urban train system).
Here, 'metrô' is used as a noun referring to the means of transportation, the subway or underground.
Eu pego o metrô para ir ao trabalho todos os dias.
I take the subway to go to work every day.
In this sentence, 'metrô' is again a noun but emphasizes the condition of the subway system at a particular time.
O metrô estava lotado hoje de manhã.
The subway was crowded this morning.
Here 'de metrô' is a phrase using 'metrô' and indicates a preference for the mode of transportation.