Feeling pressure, bitterness consumes one (12)
I believe the answer is:
presentiment
'feeling' is the definition.
(I know that presentiment is a feeling)
'pressure bitterness consumes one' is the wordplay.
'pressure' becomes 'p' (scientific abbreviation).
'bitterness' becomes 'resentment' (synonyms).
'consumes' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'resentment' enclosing 'i' is 'resentiment'.
'p'+'resentiment'='PRESENTIMENT'
(Other definitions for presentiment that I've seen before include "An intuitive feeling" , "bad feeling" , "Feeling of apprehension" , "Intuitive foreboding" .)