To sing wildly must mean something (4)
I believe the answer is:
sign
'must mean something' is the definition.
I can't judge whether this definition defines the answer.
'to sing wildly' is the wordplay.
'wildly' indicates anagramming the letters.
'sing' is an anagram of 'SIGN'.
Can you help me to learn more?
(Other definitions for sign that I've seen before include "Omen or indication" , "Leo, for instance" , "Traffic control - to write one's name" , "Communicate to the deaf" , "Any of the 12 divisions of the Zodiac" .)