The most common and most likely answer to this crossword clue is the 6 letter word HYDROS
I've seen this crossword clue in The Guardian
H
Y
D
R
O
S
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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 HYDROS mean?
HYDROS noun- Hydroelectric power
- Electrical power supply; specifically, electrical power provided by a utility (as a publicly-owned one); payment or bills for this.
- A spa.
- A floatplane, an airplane specialized for operating on water, having pontoon floats instead of skids or wheels