Insult 51 in complaint is 'an inability to accept the truth' (9)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
disbelief
'an inability to accept the truth' is the definition.
I can't tell whether this defines the answer.
'insult 51 in complaint' is the wordplay.
'insult' becomes 'dis' (shortened form of 'disrespect' - slang).
'5d' becomes 'LI' (roman numeral).
'in' indicates putting letters inside.
'complaint' becomes 'beef' (beef can mean a complaint or objection).
'li' inserted into 'beef' is 'belief'.
'dis'+'belief'='DISBELIEF'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for disbelief that I've seen before include "Refusal to advance credit" , "Lack of faith" , "having exhausted trust fund?" , "Incredulity" .)