Gloomy and glum are the opposite of cheerful. They begin with the letter G.
Angry
The opposite of "bright" is usually "dim." The "g" may be incorrect.
A four letter word that is opposite of received and starts with the letter g is gave.
Glut
adding its opposite?
The three-letter opposite of cold is "hot." I realize that doesn't end in "g."
Given
wag
gentle
glad
good