Fully means completely or entirely, with nothing left out or held back. When you fully understand something, you grasp every part of it. When a glass is fully empty, there's not a single drop left inside.

The word describes doing something all the way, not halfway. A battery that's fully charged has reached 100 percent power. A theater that's fully booked has sold every seat. When you're fully committed to learning piano, you practice regularly and take it seriously, rather than just dabbling.

You'll often see fully paired with words ending in -ed to describe complete states: fully grown, fully cooked, fully prepared. A fully grown oak tree has reached its mature height. Chicken should be fully cooked all the way through to be safe to eat.

The opposite of fully is partially or partly, which means only some of the way. If you're only partially paying attention in class, part of your mind is elsewhere. But when you're fully focused, you're giving something your complete attention.