How can I exclude a word by using re?

[could ildg]

In re, the punctuation "^" can exclude a single character, but I want
to exclude a whole word now. for example I have a string "hi, how are
you. hello", I want to extract all the part before the world "hello",
I can't use ".*[^hello]" because "^" only exclude single char "h" or
"e" or "l" or "o". Will somebody tell me how to do it? Thanks.
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