Millions in outside support for climbers barking up the wrong tree (8)
I believe the answer is:
mistaken
'climbers barking up the wrong tree' is the definition.
I can't tell whether this definition defines the answer.
'millions in outside support' is the wordplay.
'millions' becomes 'm' (abbreviation).
'outside' means one lot of letters goes inside another.
'support' becomes 'stake' (I have seen 'stout support' mean 'stake' so perhaps 'support' could also mean 'stake').
'in' placed around 'stake' is 'istaken'.
'm'+'istaken'='MISTAKEN'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for mistaken that I've seen before include "Erroneous" , "'Wrong, misguided (8)'" , "Wrong-headed" , "Wrong in opinion, judgment etc." , "Wrongly understood" .)