Gaff has the following meanings:
1. An iron hook with a handle for landing large fish.
Usage Example: although he had the gaff lying next to him, he did not even try to lift it up.
2. Harsh treatment or criticism.
Usage Example: The workers could bear the gaff of the management if they had a wage hike.

Gaffe is a social blunder; faux pas.
Usage Example: Her gaffe was unforgivable by all present at the gathering.

Gain means
1. To get (something desired), especially as a result of one's efforts.
Usage Example: She had to gain permission of the principal to sit in the exam.
2. To acquire as an increase or addition.
Usage Example: It is very easy to gain weight , but very difficult to lose it.
3. To win (someone) to one's own side or point of view; persuade.
Usage Example: He made a tremendous amount of effort to gain the support of his colleagues.

Gainly means graceful; comely; handsome. 
Usage Example: A gainly young man came to receive us at the station.

Gait means a manner of walking, stepping, or running.
Usage Example: The old man carrying the elegant walking stick had an impressive gait.

Gate means an opening to allow passage into or out of an enclosed place.
Usage Example: There was fencing all around the house and a huge iron gate.

Galleon is a large sailing ship having three or more masts.
Usage Example: They were ordered to board the fifth galleon on the right side of the dock.

Gallon is a unit of capacity equal to 231 cubic inches.
Usage Example: To make orange juice add 3 pounds of sugar to every gallon of juice.

Galloon means a braid or trimming of worsted, silk or rayon tinsel, gold or silver, etc.
Usage Example: The galloon was executed in a lighter tone than the fabric.

Gambit means any maneuver by which one seeks to gain an advantage.
Usage Example: After having settled down he decided to venture into a conversational gambit.

Gamut means the entire scale or range.
Usage Example: Due to anger his face ran the gamut from pink to ashen white and vice versa.

Gamble means:
1. To play at any game of chance for money or other stakes.
Usage Example: He likes to gamble be it for high or low stakes.
2. To take a chance on; venture; risk.
Usage Example: It is not advisable to gamble one's future on a whim.

Gambol means to skip about, as in dancing or playing; frolic.
Usage Example: It is such fun to watch the young lambs gambol in the green grass.

Gap means:
1. A break or opening, as in a fence, wall, or military line; breach.
Usage Example: cold air is seeping through the gap in the door and its frame.
2. A wide divergence or difference; disparity.
Usage Example: There is a large gap between the rich and the poor which is unlikely to be filled.
3. A difference or disparity in attitudes, perceptions, character, or development.
Usage Example: These days the generation gap is getting less due to fast moving technology.

Gape means to stare with open mouth, as in wonder.
Usage Example: Don't gape, pay the bill!

Generic means applicable or referring to a whole class or group; general.
Usage Example: Normally people would buy generic cereals as they cost less.

Genetic means of or relating to genetics, genes, or the origin of something.
Usage Example: Cultural evolution is better and faster than genetic evolution.

Genius means a person with exceptional ability, esp. of a highly original kind.
Usage Example: Mozart was a prolific genius composed many symphonies and concertos.

Genus means any of the taxonomic groups into which a family is divided and which contains one or more species.
Usage Example: Felidae (cats, leopard, cheetah, and lion) is a genus of the cat family.

Genteel means well-bred or refined; polite; elegant; stylish.
Usage Example: The city was apparently full of rich and genteel people.

Gentle means kindly; amiable/ moderate.
Usage Example: Her voice was gentle and kind.