Six day nurses run practice of excellence (6)
I believe the answer is:
virtue
'practice of excellence' is the definition.
'virtue' can be an answer for 'excellence' (I've seen this before). I'm unsure of the 'practice of' bit.
'six day nurses run' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'day' becomes 'tue' (abbreviation for Tuesday).
'nurses' means one lot of letters goes inside another (nurse can mean to hold onto or harbour).
'run' becomes 'r' (cricket abbreviation).
'vi'+'tue'='vitue'
'vitue' placed around 'r' is 'VIRTUE'.
Can you help me to learn more?
(Other definitions for virtue that I've seen before include "Rectitude" , "Good trait" , "Admirable quality" , "Admirable feature" , "''....is it's own reward'' (6)" .)