Wonderful publication: Guardian, finally providing Matilda with little money! (11)
I believe the answer is:
magnificent
'wonderful' is the definition.
(I know that wonderful can be written as magnificent)
'publication guardian finally providing matilda with little money' is the wordplay.
'publication' becomes 'mag' (abbreviation for magazine).
'finally' indicates one should take the final letters.
'providing' becomes 'if' (eg 'providing it's sunny' means 'if it's sunny').
'matilda with' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'little money' becomes 'cent' (coin of little value).
The last letter of 'guardian' is 'n'.
'mag'+'n'+'if'+'i'+'cent'='MAGNIFICENT'
(Other definitions for magnificent that I've seen before include "Very beautiful, impressive" , "like Lorenzo de' Medici" , "brilliant" , "Seven in picture" , "Superb, imposing" .)