They tend the sick (6)
I believe the answer is:
nurses
'they tend the sick' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nurses that I've seen before include "Carers of the sick" , "Tends to needs of sick person" , "Cares for the sick." , "workers in colonies" , "Matrons, midwives etc." .)