By providing parking for royalty (3)
I believe the answer is:
per
'by' is the definition.
(I've seen this in another clue)
'parking for royalty' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'for' says to put letters next to each other.
'royalty' becomes 'ER' (abbreviation for Elizabeth Regina).
'p'+'er'='PER'
'providing' is the link.
(Other definitions for per that I've seen before include "For each or every" , "Preposition indicating by means of" , "Preposition meaning for each" , "According to" .)