english
1
general::
Available if summoned, as in Medical residents are required to be on call at least three nights a week. This expression originated as at call in the late 1500s. Also see AT SOMEONE'S BECK AND CALL.
American Heritage Idioms
2
general::
Phrase(s): on call ready to serve when called. • I live a very hard life. I’m on call twenty hours a day. • I’m sorry, but I can’t go out tonight. I’m on call at the hospital.
McGrawhill's American Idioms And Phrasal Verbs