Do I use ''pass'' or ''past'' in this sentence - I slept pass morning?

Answer 1

I'm not sure what you are trying to say here, but you could reword it to say "I slept through the morning." or "I slept during the morning." In a literal use of the sentence you give, you would use past.

I slept past morning.

Answer 2

You should use "past" in this sentence. It should be written as: "I slept past morning." This indicates that morning had already ended or that you slept through the morning.