Understand a valley surrounds it (5)
I believe the answer is:
glean
'understand' is the definition.
Although both the answer and definition are verbs in their base form, I don't understand how one could define the other.
'a valley surrounds it' is the wordplay.
'a valley' becomes 'glen' (glen is a kind of valley).
'surrounds' indicates putting letters inside.
'it' becomes 'a' (I can't explain this - if you can you should believe this answer much more).
'glen' placed around 'a' is 'GLEAN'.
Can you help me to learn more?
(Other definitions for glean that I've seen before include "Gather; collect gradually" , "Gather after reaping" , "Gather (slowly, with difficulty)" , "Gather (after reapers)" , "Gather (grain) after a harvest" .)