1. Lack of knowledge or mental capacity; idiocy; foolishness 
2. An idiom; a form, mode of expression, or signification, peculiar to a language

Derived forms: idiotisms

• undignified
• undiluted
• undiminished
• undimmed
• undine
• undiplomatic
• undiplomatically
• undirected
• undiscerning
• undischarged
• undiscipline
• undisciplined
• undisclosed
• undiscouraged
• undiscoverable
• undiscovered
• undiscriminating
• undisguised
• undismayed
• undisputable
• undisputed
• undisputedly
• undissolved
• undistinguishable
• undistinguished