join up
US /dʒɔɪn ʌp/
UK /dʒɔɪn ʌp/
1.
to become a member of an organization, club, or group
:
•
He decided to join up with the local environmental group.
•
Many young people join up for various social causes.
2.
to join the armed forces
:
•
He decided to join up right after high school.
•
Many young men were encouraged to join up during the war.