They tend to be in hospital! (6)
I believe the answer is:
nurses
'they' is the definition.
Both the definition and answer are plural nouns.
Perhaps there's an association between them I don't understand?
'tend to be in hospital' is the wordplay.
'tend to' becomes 'nurse' (I've seen this in another clue).
'be in hospital' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'nurse'+'s'='NURSES'
Can you help me to learn more?
(Other definitions for nurses that I've seen before include "Looks after" , "Carers of the sick" , "Ministering angels" , "Takes care of the sick" , "They tend the sick" .)