Pointer to a royal line (5)
I believe the answer is:
arrow
'pointer' is the definition.
('arrow' can be a synonym of 'pointer')
'a royal line' is the wordplay.
'royal' becomes 'r' (abbreviation).
'line' becomes 'row' (row is a kind of line**).
'a'+'r'+'row'='ARROW'
'to' acts as a link.
(Other definitions for arrow that I've seen before include "Quarrel, fired from crossbow" , "Sharp-tipped missile" , "Type of projectile" , "Pointed projectile" , "It caught Harold's eye" .)