Background:
Gnomes are of a similar height to Halflings, only of slightly larger build, and where Halflings are wanderers, happy-go-lucky, Gnomes are stolid and sensible.
Most Gnomes are to be found in the forests. They share their love of woodlands and all life with Elven folk, and indeed some other traits. They are a minor-magical people, and while lacking the far superior skills of Elves, they can use some cantrips to ensure that they are undisturbed and to help their fellow forest-dwelling creatures.
Gnomes are generally placid creatures, but surprisingly stubborn and slow to give way in the face of evil. Obviously in combat they use such weapons suited to their short stature, such as short-swords and war-hammers. They also wear some sort of an armour most of the time, prudent as they are.
Having said this, Gnomes are not natural warriors. They have a natural empathy with living beings that even most Elves do not share. Many become Druids, living and tending to the forestlife that they love. Few obey the call of the warrior, meaning that the number of Gnomes in the Irregulars are small.
The origins of Gnomes are uncertain, to be sure. There seem to be three lines of reasoning on this. One is that they were simply created by the Gods, but stayed in hiding until later on the time-scale. The second is that they were a tribe of Halflings that simply settled down.
The last, and possibly the most widely believed, is that they were once Dwarfs. They certainly share some physical resemblence to Dwarven folk, in height and other appearance. However their obsession for preserving life is not shared by their Dwarven cousins, and certainly no self-respecting Dwarf would spend his life in company with an Elf! Certainly Dwarves are remarkably close-mouthed on the situation, and the Gnomes themselves either don't know or won't tell.
Role-playing:
Gnomes are irritable, grumpy creatures when disturbed, but have good common sense. They are normally helpful to adventurers when awake, but do not want to be disturbed, and will go out of their way to make sure that they aren't.
Advantages - increased Wisdom, some minor magical cantrips are easier to learn, stubborness, resistance to minor magic and fear.
Disadvantages - decreased Charisma and Dexterity.
Specialized Racial Class - Druid.
