iufijifidafhudfhafa
The longest ones I could find in Webster's Second International dictionary are 17 letters long: antiagglutinating autoagglutinating
Another word starting with g is gloominess
gabbroic
gynotikolobomassophile
There are two at 21 letters each, but looks like gastroenteroanastomosis wins at 23 letters: 23 gastroenteroanastomosis 21 gastroenterocolostomy 21 glossolabiopharyngeal
The longest word in the English language beginning with the letter G is "gastroenterocolitises," which is a plural form of "gastroenterocolitis." Gastroenterocolitis is the inflammation of the stomach, small intestine, and colon. The plural form refers to multiple instances of this condition.
killing
good
Geometry.
gloomy
global
Ghoul.