Goat is able to get a water-boiler (5-3)
I believe the answer is:
billy-can
'get a water-boiler' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'goat is able' is the wordplay.
'goat' becomes 'billy' (billy goat is a kind of goat).
'is able' becomes 'can' (if you can do something, you are able to do it).
'billy'+'can'='BILLY-CAN'
'to' acts as a link.
Can you help me to learn more?
(Another definition for billy-can that I've seen is " Campfire pot".)