The first one acquired new weight (5)
I believe the answer is:
tonne
'weight' is the definition.
(I've seen this before)
'the first one acquired new' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'first one' becomes 'o' (nst letter of 'one').
'acquired new' becomes 'nne' (I can't justify this - if you can you should believe this answer much more).
't'+'o'+'nne'='TONNE'
Can you help me to learn more?
(Other definitions for tonne that I've seen before include "Metric weight unit" , "Heavyweight" , "A thousand kilogrammes" , "1000 kilograms" , "One thousand kilograms" .)