Weighty letter to Lois, perhaps (5)

I believe the answer is:

kilos

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'weighty letter to lois perhaps' is the definition.
I can't judge whether this definition defines the answer.

'letter to lois perhaps' is the wordplay.
'letter' becomes 'k' ().
'perhaps' indicates an anagram.
'lois' is an anagram of 'ilos'.
'k'+'ilos'='KILOS'

Can you help me to learn more?

(Other definitions for kilos that I've seen before include "Metric weights" , "Units of mass" , "Units of weight in metric system" , "Units of weight of 1000 grams" .)

I've seen this clue in the Evening Standard.

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