I had a go at starting that hare a few posts ago. It's the old solipsist thing. You know YOU feel, otherwise you rule yourself out of the discussion. But you don't know if anything else feels, and there's no way you can find out. The Turing test.So "sentienht" means simply "feels things like I do". You can dress that as fancy as you like, but for a' that an' a' that...

On the other hand, you can do comparisons- a dog "begs" for treats, so we treat the dog as something with communicable wants and therefore feelings in some way comparable to ours. And go on "down the scale", mice, chickens, lizards, worms, centipedes, spiders..... eventually you (might) conclude that they are more similar to a machine executing an algorithm than to a person with feelings, hopes, desires, fears, intentions and the rest of the paraphernalia of sentience.

Sentience ends with a full stop, or a question mark...