Yearn to have a bash at, though it's unlikely to be successful (4,4)
I believe the answer is:
long shot
'though it's unlikely to be successful' is the definition.
I can't tell whether this defines the answer.
'yearn to have a bash' is the wordplay.
'yearn' becomes 'long-' (synonyms).
'to have' says to put letters next to each other.
'a bash' becomes 'shot' (both can mean an attempt).
'long'+'shot'='LONG SHOT'
'at' is the link.
Can you help me to learn more?
(Other definitions for long shot that I've seen before include "Poor prospect" , "A bet on outsider" , "Contestant unlikely to win" , "Something with slight chance of success" , "Very uncertain venture" .)