Crossword Genius

Corresponding without opening case for source (7)

Ross

I believe the answer is:

elative

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

'case for source' is the definition.
'elative' can be an answer for 'case' (thesaurus). I'm not certain of the 'for source' bit.

I can't explain the rest of the clue.

Can you help me to learn more?

I've seen this clue in The Times and The Sunday Times.
Want a hint initially instead of a full solution? Install my app