Sound of mind, but just at heart, on consideration (6)
I believe the answer is:
intact
'sound' is the definition.
(I've seen this before)
'mind but just at heart on consideration' is the wordplay.
I cannot quite understand how this works, but
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is present in the answer.
'consideration' could be 'tact' (tact is a kind of consideration) and 'tact' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for intact that I've seen before include "Undamaged, unimpaired" , "Complete - unbroken" , "Entire, undamaged" , "Whole and complete" , "Not broken or damaged" .)