Question

The loss of water as water vapour from the aerial parts of a plant is known as

Answer 1

it is known as transpiration

Answer 2

This process as described by you in your question is known as transpiration. It can be stomatal transpiration, lenticular transpiration or cuticular transpiration.
Stomatal occurs through stomata,
Lenticular occurs through lenticles and
Cuticular occurs through cuticle or waxy coating of plants.

Thanks.