1 [intransitive and transitive]
to become twice as big or twice as much, or to make something twice as big or twice as much
double in size/number/value etc
Within two years the company had doubled in size.
The church has doubled its membership in the last five years.
double the size/number/amount etc (of something)
A promise was given to double the number of police on duty.
2 [transitive] also double over/up
to fold something in half:
Take a sheet of paper and double it over.
to hit the ball far enough to get to second base in a game of baseball
double as somebody/somethingphrasal verb
The school doubled as a hospital during the war.
double backphrasal verb
The driver doubled back and headed for Howard Bay.
double back on yourself
We kept getting lost and having to double back on ourselves.
double upphrasal verb
1 also double over
to suddenly bend over at the waist because you are laughing so much or are in pain:
Emilio doubled over, grabbing his leg.
be doubled up/over with laughter/pain etc
Both the girls were doubled up with laughter.
to share something, especially a bedroom
double up with
You'll have to double up with Susie while your aunt is here.