Show sorrow when lent only about a thousand (6)

I believe the answer is:

lament

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'show' is the definition.
(I have seen 'Show of sorrow' mean 'lament' so perhaps 'show' could also mean 'lament')

'only about a thousand' is the wordplay.
'only' becomes 'lent' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'thousand' becomes 'm' (Roman numeral for a thousand).
'a'+'m'='am'
'lent' enclosing 'am' is 'LAMENT'.

'sorrow when lent' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for lament that I've seen before include "Cry of sorrow" , "Expression of sorrow" , "Complain" , "Express grief" , "Mourn , bewail the loss of" .)

I've seen this clue in the Evening Standard.

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