Thousands have grit (4)
I believe the answer is:
sand
'grit' is the definition.
(synonyms)
'thousands have' is the wordplay.
'have' indicates the answer is hidden within the clue.
'SAND' is hidden in the letters of 'thousands'.
(Other definitions for sand that I've seen before include "lover of Chopin" , "Loose grains" , "Shore grains" , "Grains of quartz" , "Egg timer grains" .)