Get gnu gun, guy!
The opposite of "bright" is usually "dim." The "g" may be incorrect.
Geometry.
gaininggallonsgambledgardensgarmentgetawaygatewaygathersgeneralgentilegesturegettingghastlygiraffegirlishglassesglimmerglistenglorifygolfinggoslingglowinggradinggrantedglaringgleefulgloatedgovernsgravitygreatlygrowinggravelygrantedgreetedgravinggriffingrimacegrizzlygrosslygroomedgroomergroovedgrufflygrumblegruntedguessedgunshotguzzledgushinggutting
Gondola is a type of boat. It begins with the letter g.
Gannet
grebe
GOD
glory
Goul ? :)
The only real word that fits this is sag.Sag: To sink or bend.
Gash