In supermarket ran checkout section (7)
I believe the answer is:
tranche
'section' is the definition.
(a tranche is a section or portion of something)
'in supermarket ran checkout' is the wordplay.
'in' indicates a hidden word.
'TRANCHE' is hidden within 'supermarket ran checkout'.
(Other definitions for tranche that I've seen before include "Portion, slice" , "Portion of something, money perhaps" , "issue of shares, perhaps" , "instalment of shares" , "one particular batch?" .)