Philosophers? Most of that lot maybe fret inwardly (8)

'philosophers?' is the definition.
(those following Thomas Aquinas' philosophy)

'most of that lot maybe fret inwardly' is the wordplay.
'most of' means to remove the last letter.
'that lot' becomes 'those'.
'maybe fret' becomes 'mist' (fret is a sea mist).
'inwardly' indicates putting letters inside.
'those' with its final letter removed is 'thos'.
'thos' enclosing 'mist' is 'THOMISTS'.