Definition of "metro"

Recalling that Davide Lungo returned the van at the airport, Pizo descended the nearby stairs to the underground metro, and boarded the next metro stopping there.

2000, Frederick Parkins, The NATO Opposition, page 27

I hurry to the underground... I am waiting for the next metro; I'll take it.

2014, Lily Sergueiew, I Worked Alone: Diary of a Double Agent in World War II Europe

What we entered into here was well lit and had clean silver curvy walls that ended in nice automatic elevators that took you underground. The walls are not infested with graffiti and advertisements; they were clean and shiny. We waited on nice benches until the metro arrived.

2017, Pam Taylor, 399 Days: Our European Escapade

Informs how long the passenger has to wait for the next metro

2006, C. A. Brebbia, V. Dolezel, Urban Transport XII: Urban Transport and the Environment in the 21st Century, page 227

With the weather clear and warm for a change, I decided to catch the next metro to the outskirts of town by myself.

2008, Brandon Wilson, Along the Templar Trail: Seven Million Steps for Peace, page 75

I boarded the Yellow Line Metro, beaming with confidence. I got down at Rajiv Chowk to continue my journey towards Noida City Centre (NCC). The next metro arrived.

2015, Pratyush Sinha, Love in Metro: Story of Love and Ego

In an age of persistently high inequality, work in high-cost metros catering to the whims of the wealthy—grooming them, stretching them, feeding them, driving them—has become one of the fastest-growing industries.

2019 August 12, Derek Thompson, “America's Hot New Job Is Being a Rich Person's Servant”, in The Atlantic‎