To be undecided about; to lack confidence in; to disbelieve, to question.
Disbelief or uncertainty (about something); (countable) a particular instance of such disbelief or uncertainty.
A promise to pay a sum of money in the event that another person fails to fulfill an obligation.
One who undertakes to pay money or perform other acts in the event that his principal fails therein.
A substitute; a hostage.
Evidence; confirmation; warrant.
Certainty.
That which makes sure; that which confirms; ground of confidence or security.