V&A visitor becoming most faint (7)

I believe the answer is:

vaguest

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

'most faint' is the definition.
Both the answer and definition are superlative adjectives. Perhaps they are linked in a way I don't understand?

'va visitor' is the wordplay.
'visitor' becomes 'guest' (someone visiting a place).
'va'+'guest'='VAGUEST'

'becoming' is the link.

Can you help me to learn more?

(Another definition for vaguest that I've seen is " Least precise".)

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app