What is the meaning of Underhand?

secret; clandestine

dishonest and sneaky; done in a secret or sly manner

thrown (etc.) with the hand brought forward and up from below

with an underhand movement

in a sly, sneaky or secret manner

To toss or lob with an underhand movement.

To trick, deceive or gull.

To excavate downward in successive steps or horizontal slices while positioned above on unbroken ore.

The lower of two hands, the hand under the work.

Source: wiktionary.org