It joins any pets, if playful (6,3)
I believe the answer is:
safety pin
'it joins' is the definition.
(something which joins things together)
'any pets if playful' is the wordplay.
'playful' indicates an anagram.
'any'+'pets'+'if'='anypetsif'
'anypetsif' with letters rearranged gives 'SAFETY-PIN'.
(Other definitions for safety pin that I've seen before include "Metal fastener" , "This should not be removed" , "Fix them with this!" , "Fastening device with protective catch" , "Fixing device" .)