Lifeless King's body finally left by the Queen (5)
I believe the answer is:
inert
'lifeless' is the definition.
(thesaurus)
'king's body finally left by the queen' is the wordplay.
'king's body' becomes 'in' (I am not sure about this - if you are sure you should believe this answer much more).
'finally' indicates one should take the final letters.
'by' says to put letters next to each other.
'the queen' becomes 'er' (Elizabeth Regina).
The final letter of 'left' is 't'.
't' put after 'er' is 'ert'.
'in'+'ert'='INERT'
Can you help me to learn more?
(Other definitions for inert that I've seen before include "Without the strength to move" , "Indolent - unreactive" , "(Chem.) not reactive" , "Chemically inactive" , "Sluggish, inactive" .)