keep
Some of the questions were really difficult, but I kept calm and did my best.
A good leader is someone who can stay calm in a crisis situation.
The police are asking for all citizens to remain calm and stay in their houses.

SMART Vocabulary: related words and phrases

Calm and relaxed
(as) cool as a cucumberidiom
at (your) leisureidiom
be at peace with the worldidiom
biddable
calmly
easy come, easy goidiom
easy-going
equilibrium
fluidly
free-flowing
peaceably
peacefully
peacefulness
placable
placid
uninhibited
unpressured
unpressurized
unruffled
unshockable