The most common and most likely answer to this crossword clue is the 5 letter word FIRTH
I've seen this crossword clue in The Daily Telegraph
F
I
R
T
H
More clues leading to the result FIRTH
Buddy explains!
The straight part
We know that "Estuary" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case estuary = firth.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 FIRTH mean?
FIRTH noun- An arm or inlet of the sea; a river estuary.
- An arm or inlet of the sea; a river estuary.
- Peace; security.
- Sanctuary, asylum.
- A forest or wood; woodland generally.
- Land with mostly undergrowth and few trees; also, land in between forests or woods; pastureland which is not in use.
- Brushwood or undergrowth, sometimes in the form of a hedge.
- A hedge, especially one made from brushwood which has been wattled; also, a movable frame made from wattled branches, a hurdle.
- A kind of weir made from wattled branches for catching fish.