Yes, surer is a Scrabble word!

Adjective

1. Having or feeling no doubt or uncertainty; confident and assured

2. Exercising or taking care great enough to bring assurance

3. Certain to occur; destined or inevitable

4. Physically secure or dependable

5. Reliable in operation or effect

6. (of persons) worthy of trust or confidence

7. Infallible or unfailing

8. Certain not to fail

9. Impossible to doubt or dispute