On the one hand quite justified (5)
I believe the answer is:
right
'justified' is the definition.
(thesaurus)
'on the one hand quite' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'hand' could be 'r' (abbreviation for right, as in the right-hand side) and 'r' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for right that I've seen before include "''The customer is always .....''" , "Morally good; rectify" , "Morally correct" , "one side" , "Punch" .)