The most common and most likely answer to this crossword clue is the 4 letter word CLEW
I've seen this crossword clue in The Daily Telegraph
C
L
E
W
Buddy explains!
The straight part
We know that "for hanging a hammock" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case for hanging a hammock = clew.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CLEW mean?
CLEW noun- A roughly spherical mass or body.
- A ball of thread or yarn.
- Yarn or thread as used to guide one's way through a maze or labyrinth; a guide, a clue.
- The lower corner(s) of a sail to which a sheet is attached for trimming the sail (adjusting its position relative to the wind); the metal loop or cringle in the corner of the sail, to which the sheet is attached. (on a triangular sail) The trailing corner relative to the wind direction.
- (in the plural) The sheets so attached to a sail.
- (in the plural) The cords suspending a hammock.
- To roll into a ball
- (transitive and intransitive) to raise the lower corner(s) of (a sail)
- A strand of yarn etc. as used to guide one through a labyrinth; something which points the way, a guide.
- Information which may lead one to a certain point or conclusion.
- An object or a kind of indication which may be used as evidence.
- Insight or understanding ("to have a clue [about]" or "to have clue". See have a clue, clue stick)