4 words for BT 1–2 letters

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1 letter (2)

b t
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2 letters (2)

bt tb
Sickness – Sartre’s first novel
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Hint 1 meaning
Seasickness; hence, any similar sickness of the stomach accompanied with a propensity to vomit; qualm; squeamishness of the stomach; loathing.
Hint 2 anagram
NEUASA
Hint 3 another clue
PERPLEXED state
19 +1