Summon an errand boy (4)
I believe the answer is:
page
This clue is a double definition.
'summon' is the first definition.
(I know that page is a kind of summon)
'an errand boy' is the second definition.
(I know that page is a type of errand boy)
(Other definitions for page that I've seen before include "Young attendant for part of a book" , "Leaf; call over PA system" , "Kind of leaf, or boy in old court" , "lad wanted to run errands" , "Youth acting as a knight's attendant" .)