At first, rent handled in old money (5)
I believe the answer is:
rhino
'money' is the definition.
(I've seen this before)
'at first rent handled in old' is the wordplay.
'at first' indicates taking the first letters.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
The initial letters of 'rent handled' is 'rh'.
'rh'+'in'+'o'='RHINO'
(Other definitions for rhino that I've seen before include "Horned animal; money (slang)" , "Hi, Ron! (anag)" , "Endangered wildlife" , "Thick-skinned beast" , "This beast may make a charge" .)