River surrounded by support under dry conditions (4)
I believe the answer is:
arid
'dry conditions' is the definition.
'arid' can be an answer for 'dry' (I've seen this before). I am unsure of the 'conditions' bit.
'river surrounded by support under' is the wordplay.
'river' becomes 'r' (abbreviation).
'surrounded by' indicates putting letters inside.
'support under' becomes 'aid' (to aid is to help or support. I am not sure about the 'under' bit.).
'r' inserted inside 'aid' is 'ARID'.
Can you help me to learn more?
(Other definitions for arid that I've seen before include "Parched and barren" , "Very dry; uninteresting" , "Dry and withered" , "(Of an area) very dry" , "(Of climate) dry" .)