Single male with terrible clothing is a fool (8)
I believe the answer is:
bonehead
'single male' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'terrible clothing is a fool' is the wordplay.
'terrible' becomes 'bad' (similar in meaning).
'clothing' indicates putting letters inside (some letters cover up or clothe others).
'is a' becomes 'one'.
'fool' becomes 'he' (I can't justify this - if you can you should give a lot more credence to this answer).
'one'+'he'='onehe'
'bad' placed around 'onehe' is 'BONEHEAD'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for bonehead that I've seen before include "Numbskull" , "Fool" , "dope" , "stupid leader" , "Stupid person (colloq.)" .)