Saturate monarch in paved complex (7)
I believe the answer is:
pervade
'saturate' is the definition.
(thesaurus)
'monarch in paved complex' is the wordplay.
'monarch' becomes 'er' (abbreviation for Elizabeth Regina, British Queen).
'in' indicates putting letters inside.
'complex' indicates an anagram.
'paved' with letters rearranged gives 'pvade'.
'er' inserted within 'pvade' is 'PERVADE'.
(Other definitions for pervade that I've seen before include "Diffuse through the whole" , "Permeate" , "Spread throughout" , "Occur in every part of" , "Suffuse" .)