Stand or stumble on a piece of wood (6)
I believe the answer is:
tripod
'stand' is the definition.
(I know that tripod is a type of stand)
'stumble on a piece of wood' is the wordplay.
'stumble' becomes 'trip' (synonyms).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'a piece of wood' becomes 'od' (I can't justify this - if you can you should believe this answer much more).
'trip'+'od'='TRIPOD'
'or' is the link.
Can you help me to learn more?
(Other definitions for tripod that I've seen before include "Three-legged stand as for camera" , "one appears to have three legs!" , "oral test at school" , "Stand on three legs" , "Pay heed" .)