Frail pet cried out (8)
I believe the answer is:
decrepit
'frail' is the definition.
('decrepit' can be similar in meaning to 'frail')
'pet cried out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'pet'+'cried'='petcried'
'petcried' is an anagram of 'DECREPIT'.
(Other definitions for decrepit that I've seen before include "Pet cried (anag) - worn out" , "Dilapidated, made weak by age" , "like a crate?" , "Depicter in state of dilapidation" , "Worn out; infirm" .)