Definition:

lacking intelligence: stupid

Example:

"Gormless, unhelpful and poorly trained shop staff create merry hell for customers who are simply exercising their legal rights to a repair, refund or replacement." – Sam Dunn, Two Pennies Worth blog, March 22, 2011

About the word:

The word gaum exists in some English dialects and means "attention or understanding." Someone without gaum (or gorm) lacks understanding.