In most dialects, possibly, it means –perfect” (5)
I believe the answer is:
'perfect' is the definition.
(similar in meaning)
'in most dialects possibly' is the wordplay.
'most' means to remove the last letter.
'dialects possibly' becomes 'deal' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' with its last letter taken off is 'i'.
'it means' acts as a link.
Can you help me to learn more?
(Other definitions for ideal that I've seen before include "Perfect but perhaps unlikely to become reality" , "Paradigm" , "highly desirable" , "supreme" , "fine" .)