Steady weather set to turn stormy (10)

I believe the answer is:

sweetheart

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

Here is my best explanation:

'steady' is the definition.
(synonyms)

'weather set to turn stormy' is the wordplay.
'weather set' anagrams to 'SWEETHEART'.
However, I'm unsure how the anagram is indicated.

Can you help me to learn more?

This clue was last seen in The Telegraph