Possibly frees part of the sail (5)
I believe the answer is:
reefs
'possibly frees part of the sail' is the definition.
I can't tell whether this definition defines the answer.
'possibly frees' is the wordplay.
'possibly' is an anagram indicator.
'frees' with letters rearranged gives 'REEFS'.
Can you help me to learn more?
(Other definitions for reefs that I've seen before include "Ridges of rock or sand beneath sea surface" , "Groups of submerged rock" , "coral banks" , "Submerged ridges of rock or coral near the surface of water" .)