Weights initially kept Lois fresh (5)
I believe the answer is:
kilos
'weights' is the definition.
(I have seen 'Metric weights ' mean 'kilos' so perhaps 'weights' could also mean 'kilos')
'initially kept lois fresh' is the wordplay.
'initially' indicates taking the first letters.
'fresh' indicates an anagram.
The initial letter of 'kept' is 'k'.
'lois' is an anagram of 'ilos'.
'k'+'ilos'='KILOS'
(Other definitions for kilos that I've seen before include "Metric weights" , "Units of weight in metric system" , "Units of weight of 1000 grams" , "Units of mass" .)