Normal clue lacking definition ultimately becomes elementary? (9)
I believe the answer is:
molecular
'elementary?' is the definition.
'normal clue lacking definition ultimately' is the wordplay.
I cannot really understand how this works, but
an anagram of 'clue' is 'lecu' which is within the answer.
The remaining letters 'molar' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
'becomes' is the link.
(Other definitions for molecular that I've seen before include "Relating to groups of atoms bonded together" , "Relating to the smallest particles of a substance" , "Dealing with small particles" .)