Hat left out in alcove (5)
I believe the answer is:
bower
'alcove' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for bower that I've seen before include "Garden space shaded from the sun by plants" , "Shaded place under trees" , "Shady shelter" , "Arbour" , "Anchor" .)