assure
v.v. to tell someone something strongly so they feel sure or less worried. You use this when you want to promise someone that a situation is okay or will be successful.
v. to state something positively or confidently to remove doubt. Transitive in nature, it requires a person as the direct object to whom the promise is made.
I assure you that the train will arrive on time.
The manager met with the staff to assure them that no jobs would be lost during the merger.
The lead architect sought to assure the board that the structural integrity of the building met all safety standards despite the recent tremors.
From Old French asseurer (Modern French assurer), from Latin ad- + securus (“secure”). Cognate with Spanish asegurar. Doublet of assecure.
The verb is transitive and requires an indirect object (the person being assured) before the 'that' clause or the direct object.
I assure that the work is doneI assure you that the work is doneAssure must be followed by a person (the object) to whom the promise is made, unlike 'ensure' or 'insure'.