One doesn't have to have them (5)
I believe the answer is:
needs
'them' is the definition.
I can't tell whether this definition defines the answer.
'one doesn't have to have' is the wordplay.
'one doesn't have' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'to' says to put letters next to each other (I've seen this in other clues).
'have' becomes 'need' (synonyms).
's' put after 'need' is 'NEEDS'.
Can you help me to learn more?
(Other definitions for needs that I've seen before include "Requires or lacks" , "Necessitates" , "Requires, is in want of" , "Misses" , "Is desperate for" .)