Cattle cross east between beginning of October and November (4)
I believe the answer is:
oxen
'cattle' is the definition.
(synonyms)
'cross east between beginning of october and november' is the wordplay.
I cannot quite see how this works, but
'cross' could be 'x' (X is cross-shaped) and 'x' is present in the answer.
'east' could be 'e' (synonyms) and 'e' is found within the answer.
'of' could be 'o' and 'o' is found within the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
No letters remain.
This explanation may well be incorrect...
(Other definitions for oxen that I've seen before include "(E.g. draught) cattle" , "Bovine animals, in yoke" , "Heavy cattle" , "Bovine creatures" , "Cows and bulls" .)