Definify.com

Webster 1828 Edition

, a.

Not guarded; not watched.

Not defended; having no guard.

Careless; negligent; not attentive to danger; not cautious; as, to be unguarded in conversation.

Negligently said or done; not done or spoken with caution; as an unguarded expression or action.

unguarded ‎(comparative more unguarded, superlative most unguarded)

Having no guard or protection; vulnerable.
The unguarded gatehouse was soon taken by the invading army.
Displaying a lack of caution or thought.
I let out her secret in an unguarded moment.