Crawler, when sap flows (3)
I believe the answer is:
asp
'crawler' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'sap flows' is the wordplay.
'flows' indicates anagramming the letters (I've seen 'flow' mean this (to flow can mean to move around)).
'sap' is an anagram of 'ASP'.
'when' is the link.
Can you help me to learn more?
(Other definitions for asp that I've seen before include "Snake, killed Cleopatra" , "Cleopatra's poisoner" , "snake appears" , "Small poisonous snake" , "This Egyptian killer" .)