1
general::
Knowledge in advance enables one to be prepared, as in Let me know when he's in town so I can take the phone off the hook? forewarned is forearmed. This expression originated as a Latin proverb, Praemonitus, praemunitus, which was translated into English by the early 1500s. It soon was put to broader use than its original military applications.
American Heritage Idioms
2
general::
Phrase(s): Forewarned is forearmed.
Prov. If you know about something beforehand, you can prepare for it. • Before you meet Lily, I should tell you that she’s a little eccentric. Forewarned is forearmed, right? • Check the temperature before you go outside. Forewarned is forearmed.
McGrawhill's American Idioms And Phrasal Verbs