Lecturer welcoming the old senior member (5)
I believe the answer is:
doyen
'senior member' is the definition.
(a senior or respected figure)
'lecturer welcoming the old' is the wordplay.
'lecturer' becomes 'don' (don is a term for an academic).
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'the old' becomes 'ye' (resembles a historical spelling of 'the').
'don' enclosing 'ye' is 'DOYEN'.
(Other definitions for doyen that I've seen before include "Most prominent expert" , "Senior member of a professional group" , "Man who is the senior in his profession" , "Most valued prof, eg" , "Prominent person in a particular field" .)