A number claim it is changeable like the weather (8)
I believe the answer is:
climatic
'like the weather' is the definition.
(I've seen this before)
'a number claim it is changeable' is the wordplay.
'a number' becomes 'c' (C is an example).
'is changeable' indicates an anagram.
'claim'+'it'='claimit'
'claimit' is an anagram of 'limatic'.
'c'+'limatic'='CLIMATIC'
(Other definitions for climatic that I've seen before include "Like the weather" , "of prevailing conditions" , "Relating to the weather" .)