Substitute most appropriate word for following from the given options:
so deep that the bottom cannot be reached

unfathomable

The most appropriate word for so deep that the bottom cannot be reached is unfathomable.

• Fumble means to handle something clumsily or incompetently.
• Unfathomable means too deep or obscure to be understood.
• Conventicle means a secret or unauthorized religious meeting.
• Contrite means feeling or showing sincere regret or remorse for one's wrongdoing.