Cleaner put on short pants (7)
I believe the answer is:
shampoo
'cleaner' is the definition.
(shampoo cleans hair)
'put on short pants' is the wordplay.
'put on' becomes 'sham' (synonyms).
'short pants' becomes 'poo' (I can't justify this - if you can you should believe this answer much more).
'sham'+'poo'='SHAMPOO'
Can you help me to learn more?
(Other definitions for shampoo that I've seen before include "Oh, so Pam uses it on her hair?" , "Liquid that goes to your head?" , "Hair or carpet cleaner" , "Top cleaning product" , "Would Mao shop for this cleaner?" .)