A jumping-off place (11)
I believe the answer is:
springboard
'place' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'a jumping-off' is the wordplay.
'a jumping' becomes 'spring' (spring is a kind of jumping).
'off' becomes 'board' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'spring'+'board'='SPRINGBOARD'
Can you help me to learn more?
(Other definitions for springboard that I've seen before include "Diver's launch point" , "Help with launch" , "From which ideas may be launched" , "Flexible point of departure?" , "fresh impetus" .)