Smell from stream cut off at source (4)
I believe the answer is:
reek
'smell' is the definition.
(I know that smell can be written as reek)
'stream cut off at source' is the wordplay.
'stream' becomes 'creek' (creek is a kind of stream).
'cut off at source' means to remove the first letter (the word's source or beginning is removed).
'creek' with its initial letter removed is 'REEK'.
'from' acts as a link.
(Other definitions for reek that I've seen before include "Pong" , "Effluvium" , "Does Croagh Patrick smell?" , "Smell, like a Kerry mountain?" , "Smell unpleasant" .)