One who worked like a horse? (6)
I believe the answer is:
trojan
'one who worked' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a horse?' is the wordplay.
I cannot really understand how this works, but
'a' could be 'an' and 'an' is present in the answer.
This explanation may well be incorrect...
'like' is the link.
Can you help me to learn more?
(Other definitions for trojan that I've seen before include "Paris who abducted Helen was such a prince" , "Sort of horse" , "This war involved the kidnapping of fair Helen" , "Native of Troy" , "one typically hard-working" .)