1
general::
1. Make certain, establish something without doubt, as in Make sure all the doors are locked. It is Also put as make sure of, as in Before you make that speech, make sure of your facts. This usage was first recorded in 1565. 2. make sure of. Act so as to be certain of something, as in He wanted to make sure of his own district before seeking support elsewhere. This usage was first recorded in 1673.
American Heritage Idioms
2
general::
Phrase(s): make sure (of something)
to check something and be certain about it. • Please make sure of your facts before you write the report. • We made sure of the route we had to follow before we left. • Please double-check and make sure.
McGrawhill's American Idioms And Phrasal Verbs