Harassed press for introducing old don? (9)
I believe the answer is:
professor
'don?' is the definition.
(thesaurus)
'harassed press for introducing old' is the wordplay.
'harassed' is an anagram indicator.
'introducing' means one lot of letters goes inside another (some letters introduced or inserted into others).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'press'+'for'='pressfor'
'pressfor' is an anagram of 'professr'.
'professr' enclosing 'o' is 'PROFESSOR'.
(Other definitions for professor that I've seen before include "University lecturer" , "One holds a chair" , "Head of university department" , "Senior member of college faculty" , "Member of an academic faculty" .)