Other forms: frustratingly
Frustrating things are the ones that discourage or disappoint you. It's frustrating to finally get your driver's license only to realize you can't afford to pay for insurance on your car.
If you find people frustrating, it's often because they refuse to help or listen to you. You might find it frustrating to talk to your cranky grandfather or to be called the wrong name day after day by your forgetful English teacher. Frustrating situations are usually ones that keep you from achieving your goals. The Latin root word is frustrari, "to deceive or disappoint," from frustra, "in vain or in error."