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