Soon, one's name is unknown (4)
I believe the answer is:
anon
'soon' is the definition.
(synonyms)
'one's name is unknown' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'name' becomes 'n' (common abbreviation e.g. on forms).
'is unknown' becomes 'on' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a'+'n'+'on'='ANON'
Can you help me to learn more?
(Other definitions for anon that I've seen before include "Soon, in a little while" , "Soon, precious stone" , "In a little while (informal)" , "devoid of credit" , "Incognito (abbrev)" .)