To make sure. See Insure.
To make sure or certain
To make certain. see also insurance.
OR insure -- "ensure" means "to make certain" -- "insure" means "to provide insurance for"
To cause something to be done, either by doing it or by following up on assignments and delegations to confirm they were completed. To guarantee a particular outcome. The Laboratory uses this term when referring to situations involving direct responsibility for activities, as in the case of the Responsible Individual.
make certain of; "This nest egg will ensure a nice retirement for us"; "Preparation will guarantee success!"
be careful or certain to do something; make certain of something; "He verified that the valves were closed"; "See that the curtains are closed"; "control the quality of the product"
To make certain that something will happen