Spots river by wood (4)
I believe the answer is:
rash
'spots' is the definition.
(I've seen this before)
'river by wood' is the wordplay.
'river' becomes 'r'.
'by' means one lot of letters go next to another.
'wood' becomes 'ash' (I've seen this before).
'r'+'ash'='RASH'
(Other definitions for rash that I've seen before include "Hasty; skin disorder" , "(Armed) incursion (into another country)" , "Daredevil" , "Impulsive, hasty" , "Eruption on skin, imprudent" .)