One rubbing husband, a halfwit, up the wrong way (6)
I believe the answer is:
loofah
'one rubbing husband' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'a halfwit up the wrong way' is the wordplay.
'halfwit' becomes 'fool' (halfwit can mean a foolish person).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'the wrong way' becomes 'h' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'fool'='afool'
'afool' back-to-front is 'loofa'.
'loofa'+'h'='LOOFAH'
Can you help me to learn more?
(Other definitions for loofah that I've seen before include "Part of fruit used as bath sponge" , "Bath sponge made from dried plant fibres" , "Back scrubber" , "Bathroom sponge for washing back" , "Dried pod commonly used as bathroom sponge" .)