Hear uncle out - it's rather strong (9)
I believe the answer is:
herculean
'rather strong' is the definition.
I can't judge whether this definition defines the answer.
'hear uncle out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'hear'+'uncle'='hearuncle'
'hearuncle' with letters rearranged gives 'HERCULEAN'.
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for herculean that I've seen before include "Monumental (task)" , "Requiring very great effort" , "Enormously demanding (task)" , "Showing great strength" , "Powerful" .)