Many a white one’s seen from rocky shore (5)
I believe the answer is:
horse
'many a white one's seen' is the definition.
I can't judge whether this definition defines the answer.
'rocky shore' is the wordplay.
'rocky' is an anagram indicator.
'shore' anagrammed gives 'HORSE'.
'from' acts as a link.
(Other definitions for horse that I've seen before include "runner" , "Vaulting apparatus" , "Animal featuring in the sport of kings" , "Animal providing" , "gym apparatus" .)