Heavy individual with sour disposition (7)
I believe the answer is:
onerous
'heavy' is the definition.
(similar in meaning)
'individual with sour disposition' is the wordplay.
'individual' becomes 'one' (an individual is one person).
'with' says to put letters next to each other.
'disposition' is an anagram indicator.
'sour' anagrammed gives 'rous'.
'one'+'rous'='ONEROUS'
(Other definitions for onerous that I've seen before include "Involving a great deal of effort" , "'Burdensome, not easily borne (7)'" , "'Heavy, burdensome (7)'" , "Heavy and hard to bear" , "weight" .)