By getting a donkey out of the pit (5)
I believe the answer is:
abyss
'the pit' is the definition.
(thesaurus)
'by getting a donkey' is the wordplay.
'getting' means one lot of letters go next to another.
'donkey' becomes 'ss' (I can't justify this - if you can you should give a lot more credence to this answer).
'by' put after 'a' is 'aby'.
'aby'+'ss'='ABYSS'
'out of' acts as a link.
Can you help me to learn more?
(Other definitions for abyss that I've seen before include "crevasse" , "gaping hole" , "Hell; hole" , "Deep hole, seems bottomless" , "Measureless chasm" .)