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