Disputable nature of material is absorbing old university head (15)

'disputable nature' is the definition.
'contentiousness' can be an answer for 'nature' (contentiousness is a kind of nature). I am not sure about the 'disputable' bit.

'material is absorbing old university head' is the wordplay.
I cannot really see how this works, but
'old' could be 'o' (abbreviation) and 'o' is found in the answer.
'university' could be 'ou' and 'ou' is found in the answer.
'is' is within the answer.
'head' could be 'ness' (ness is a headland) and 'ness' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

'of' is the link.

Can you help me to learn more?