Loudly object to head's suitability (7)
I believe the answer is:
fitness
'suitability' is the definition.
(I know that fitness is a type of suitability)
'loudly object to head's' is the wordplay.
'loudly' becomes 'f' (short for forte - 'loud' in music).
'object' becomes 'it' (pronoun for an inanimate object).
'to head' becomes 'ness' (type of geographical point).
'f'+'it'+'ness'='FITNESS'
(Other definitions for fitness that I've seen before include "condition" , "Competence" , "Suitability - health" , "Well-being" , "State of good health" .)