Stretch old nurse (6)
I believe the answer is:
extend
'stretch' is the definition.
(I know that stretch is a more specific form of extend)
'old nurse' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'nurse' becomes 'tend' (tend can mean to nurse or look after).
'ex'+'tend'='EXTEND'
(Other definitions for extend that I've seen before include "Spread - offer" , "Reach out or stretch" , "make offer?" , "Enlarge, widen" , "Carry on" .)