Th as in thistle. is as in is. be as in be. First syllable emphasised.
I've only ever seen it in the context of Pyramus and
Thisbe, which was trite and shallow until Shakespeare jazzed it up. There's not much point in giving those two a happy ending! The story exists, like an early Just-So Story, to make an important lesson memorable; in this case, the message is: Don't jump to conclusions. Since they both did, with fatal results, they are memorable all right but not worth commemorating. I wouldn't use either name for a human, though
Thisbe could be OK on a cat.