Sub- (under, below)
Sub-
Under, below, or a smaller part of.
Our project report has a subheading for each section.
Submarine
A ship that travels under the sea.
Diya visited a museum submarine on the beach at Visakhapatnam.
Subway
A path or tunnel under a road.
Use the subway to cross the busy road safely.
Remember: Sub- = under: a submarine goes under the sea. In India and Britain a subway is a walkway under a road; in the USA it is a metro.