Warns suspect, describing magistrate's last solution (6)
I believe the answer is:
answer
'solution' is the definition.
(I know that solution can be written as answer)
'warns suspect describing magistrate's last' is the wordplay.
'suspect' indicates anagramming the letters (a suspicious or unusual spelling).
'describing' is an insertion indicator (describe can mean to form the outline of).
'last' suggests the final letters.
The final letter of 'magistrate' is 'e'.
'warns' is an anagram of 'answr'.
'answr' enclosing 'e' is 'ANSWER'.
(Other definitions for answer that I've seen before include "Reaction to a question" , "It could give you a" , "Reply or 8 across" , "Fulfil" , "Write back" .)