Tried to lose a crowd (4)
I believe the answer is:
herd
'crowd' is the definition.
(herding is a kind of crowding)
'tried to lose a' is the wordplay.
'tried' becomes 'heard' ('hear' can be a synonym of 'try').
'to lose' indicates named letters should be taken away.
'heard' with 'a' removed is 'HERD'.
(Other definitions for herd that I've seen before include "Drove" , "Group of cows, elephants etc" , "People in the mass" , "13 Down group" , "Crowd of cattle" .)