Capable of improving, stood regularly (2,2)
I believe the answer is:
up to
'capable of' is the definition.
(I've seen this before)
'improving stood regularly' is the wordplay.
'improving' becomes 'up' (synonyms).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'stood' are 'to'.
'up'+'to'='UP TO'
(Other definitions for up to that I've seen before include "As far as a certain point" , "Engaged in doing" , "As many as, though no more" , "Capable of" , "Busy with" .)