French salt entertains an irrational pitch… (5)
I believe the answer is:
spiel
'pitch' is the definition.
(I've seen this in another clue)
'french salt entertains an irrational' is the wordplay.
'french salt' becomes 'sel' (I've seen this in another clue).
'entertains' is an insertion indicator.
'an irrational' becomes 'pi' (an irrational number).
'sel' placed around 'pi' is 'SPIEL'.
(Other definitions for spiel that I've seen before include "Glib style of talk associated with salesmen" , "Salesperson's speech" , "Piles (anag.)" , "Glib story" , "Plausible line of talk" .)