On board, it's a slow start for Ultan, beginning at edges of reef (4)
I believe the answer is:
surf
'on board' is the definition.
The answer and definition can be both to do with motion as well as being verbs in their base form.
Perhaps they are linked in a way I don't understand?
'a slow start for ultan beginning at edges of reef' is the wordplay.
'start' suggests taking the first letters.
'for' means one lot of letters go next to another.
'beginning' says to take the initial letters.
'at' is a charade indicator (letters next to each other).
'edges of' says to hollow out the word (remove centre letters).
'reef' with its centre taken out is 'rf'.
The first letter of 'slow' is 's'.
The initial letter of 'ultan' is 'u'.
's'+'u'+'rf'='SURF'
'it's' is the link.
Can you help me to learn more?
(Other definitions for surf that I've seen before include "Ride waves - browse net" , "Shore foam" , "Foam from breakers" , "Balance on waves" , "Foam formed by breaking waves" .)