Crossword Genius

Additional indication (4)

Ross

I believe the answer is:

plus

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

This could be a double definition.

'additional' is the first definition.
(I've seen this in another clue)

'indication' is the second definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

Can you help me to learn more?

(Other definitions for plus that I've seen before include "Positive sign" , "To the French it's more" , "sign of the cross" , "As well as" , "And, arithmetically" .)

I've seen this clue in The Globe and Mail.
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