Crossword Genius

Helpful line in an advert (3)

Ross

I believe the answer is:

aid

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

'helpful line' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe there's a link between them I don't understand?

'an advert' is the wordplay.
I cannot quite see how this works, but
'an' could be 'i' (Roman numeral for one) and 'i' is present in the answer.
'advert' could be 'ad' (synonyms) and 'ad' is present in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...

'in' acts as a link.

Can you help me to learn more?

(Other definitions for aid that I've seen before include "Help, assistance" , "charity" , "Help or support" , "Relief" , "Help or succour" .)

I've seen this clue in the Evening Standard.
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