Crafty nurses understanding only a little (8)
I believe the answer is:
slightly
'only a little' is the definition.
(I've seen this before)
'crafty nurses understanding' is the wordplay.
'crafty' becomes 'sly' ('sly' can be a synonym of 'crafty').
'nurses' indicates putting letters inside.
'understanding' becomes 'light' (light is a kind of understanding**).
'sly' going around 'light' is 'SLIGHTLY'.
(Other definitions for slightly that I've seen before include "Quite!" , "To a small extent" , "to a lower degree" , "Somewhat" , "little bit" .)