Wooden leg mostly underneath chart (5)
I believe the answer is:
maple
'wooden leg mostly underneath chart' is the definition.
I can't judge whether this definition defines the answer.
'leg mostly underneath chart' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'underneath' is a charade indicator (letters next to each other) (in a down clue, some letters go under others).
'chart' becomes 'map' (synonyms).
'leg' with its final letter removed is 'le'.
'le' after 'map' is 'MAPLE'.
Can you help me to learn more?
(Other definitions for maple that I've seen before include "plant" , "Cathedral city in Devon" , "Tree of Acer genus" , "----- leaf: symbol of Canada" , "Tree: its leaf the Canadian emblem" .)