Be small in doorway? (5)
I believe the answer is:
exist
'be' is the definition.
(synonyms)
'small in doorway?' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'in' means one lot of letters goes inside another.
'doorway?' becomes 'exit' (I can't justify this - if you can you should give a lot more credence to this answer).
's' put within 'exit' is 'EXIST'.
Can you help me to learn more?
(Other definitions for exist that I've seen before include "Scrape by" , "Subsist" , "Have being or continue living" , "Get a life!" , "Be alive" .)