Crossword Genius

There are waves when it turns (4)

Ross

I believe the answer is:

tide

I'm a little stuck... Click here to teach me more about this clue!

'there are waves' is the definition.
I can't tell whether this defines the answer.

'when it turns' is the wordplay.
'when' becomes 'ed' (I am not sure about this - if you are sure you should believe this answer much more).
'turns' says the letters should be written backwards.
'ed'+'it'='edit'
'edit' reversed gives 'TIDE'.

Can you help me to learn more?

(Other definitions for tide that I've seen before include "Moon-driven sea movement" , "Current, ebb" , "Periodic rise and fall of the sea" , "Ebb and flow of water" , "Periodic water movement" .)

I've seen this clue in The Irish News.
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