Lacking experience about and knowledge about (5)
I believe the answer is:
green
'lacking' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'experience about and knowledge about' is the wordplay.
'experience about' becomes 'gr' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' becomes 'n' (common abbreviation for 'and').
'knowledge' becomes 'EE' (EE is an example).
'about' says the letters should be written in reverse.
'n'+'ee'='nee'
'nee' back-to-front is 'een'.
'gr'+'een'='GREEN'
Can you help me to learn more?
(Other definitions for green that I've seen before include "Lincoln's colour?" , "Ecologically beneficial" , "Politician perhaps" , "one of eighteen" , "Immature" .)