Use a very excellent line (5)

I believe the answer is:

avail

'use' is the definition.
(availing is a kind of using)

'a very excellent line' is the wordplay.
'very' becomes 'v' (abbreviation).
'excellent' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'line' becomes 'l' (used when specifying particular lines from a poem).
'a'+'v'+'ai'+'l'='AVAIL'

(Other definitions for avail that I've seen before include "(Of no) use or benefit" , "Medal (informal)" , "Be of service to" , "Serve a purpose" , "Make use, take advantage" .)

I've seen this clue in The Telegraph and The Sun.

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