Egghead perhaps I let call tune disastrously (12)
I believe the answer is:
intellectual
'egghead' is the definition.
(I've seen this before)
'i let call tune disastrously' is the wordplay.
'disastrously' is an anagram indicator (I've seen this in other clues).
'let'+'call'+'tune'='letcalltune'
'letcalltune' anagrammed gives 'ntellectual'.
'i'+'ntellectual'='INTELLECTUAL'
'perhaps' acts as a link.
(Other definitions for intellectual that I've seen before include "One with highly-developed mental powers" , "Scholarly" , "Thinking type" , "Academic" , "Related to rational thought processes" .)