Being green, I check energy after short nap (7)
I believe the answer is:
naivete
'being green' is the definition.
(green can mean naive or innocent)
'i check energy after short nap' is the wordplay.
'check' becomes 'vet' (I've seen this before).
'energy' becomes 'e' (physics symbol as in E=mce).
'after' means one lot of letters go next to another.
'short' means to remove the last letter.
'nap' with its final letter removed is 'na'.
'i'+'vet'+'e'='ivete'
'ivete' after 'na' is 'NAIVETE'.
(Other definitions for naivete that I've seen before include "Greenness" , "Innocence or guillibility" , "natural simplicity" , "Innocence, artlessness" , "State of inexperience (French spelling)" .)