Take on quiet, more mature university dons (8)
I believe the answer is:
shoulder
'take on' is the definition.
(I've seen this before)
'quiet more mature university dons' is the wordplay.
'quiet' becomes 'sh' (both can be said to tell someone to be quiet).
'more mature' becomes 'older' ('old' is associated in meaning with 'mature').
'university' becomes 'u' (abbreviation for university).
'dons' indicates putting letters inside (inserted letters wear or 'don' others).
'older' going around 'u' is 'oulder'.
'sh'+'oulder'='SHOULDER'
(Other definitions for shoulder that I've seen before include "See 10" , "Meat joint" , "Cut of meat" , "Part of the body (that bears burdens?)" , "On the side of the road, it might be hard" .)