Can love an expression of vigour (5-1)

I believe the answer is:

billy-o

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

'expression of vigour' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'can love' is the wordplay.
I cannot quite see how this works, but
'can' could be 'billy' (I've seen this before) and 'billy' is found in the answer.
'love' could be 'o' (love means zero in tennis) and 'o' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

'an' is the link.

Can you help me to learn more?

I've seen this clue in The Independent.

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