sure

to have a high degree of certainty

to be completely and totally certain

to be fully certain, without any doubt

to be very certain

to be completely certain (often informal)

to make extra certain of something

to ensure that something happens or is the case

to be certain about something

to have a strong personal conviction of certainty

to appear to be certain

to sound certain when speaking

to cause someone to feel certain

to be confident in something or in oneself

to be certain about a particular fact, person, or situation