WHAT IS SENTIENCE?

Someone sentient is able to feel things, or sense them. Sentient usually occurs in phrases like “sentient beings” and “sentient creatures,” making it clear that things that don’t have life don’t have feelings. Explain that to a pet rock.
Sentient comes from the Latin sentient-, “feeling,” and it describes things that are alive, able to feel and perceive, and show awareness or responsiveness. Having senses makes something sentient, or able to smell, communicate, touch, see, or hear. Whether or not plants and living things other than animals and people are sentient depends on whom you ask.
https://www.vocabulary.com/dictionary/sentient

“A sentient being is a being that, by virtue of its characteristics, has the capability of experiencing suffering, both at physical and psychological levels, regardless of the species to which it belongs.
“Only the members of the animal kingdom can be sentient, although not every animal species possesses the characteristics that would make their members be considered sentient beings.
“Sentient animals are beings that have a physical and psychological sensibility, which allows them – in the same way as humans – to experience pain and pleasure. And it is certain that they naturally seek, by all means available to them, to avoid painful experiences.”

“A conscious being’s capacity to feel and perceive; in reference to animals, it often refers to the specific ability to feel pain and suffer. ~ Leslie Bisgould
http://www.duhaime.org/LegalDictionary/S/SentientBeing.aspx