Sluggish domain without a user interface (7)
I believe the answer is:
languid
'sluggish' is the definition.
(synonyms)
'domain without a user interface' is the wordplay.
'domain' becomes 'land' (synonyms).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'a user interface' becomes 'gui' (I can't explain this - if you can you should give a lot more credence to this answer).
'land' enclosing 'gui' is 'LANGUID'.
Can you help me to learn more?
(Other definitions for languid that I've seen before include "Lauding for being listless" , "Spiritless" , "Lethargic" , "Sluggish" , "Laid-back" .)