Lacking energy please try playing instrument (8)
I believe the answer is:
psaltery
'instrument' is the definition.
(psaltery is a kind of instrument)
'lacking energy please try playing' is the wordplay.
'lacking' is a deletion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'playing' is an anagram indicator.
'please'+'try'='pleasetry'
'pleasetry' with 'e' taken away is 'plasetry'.
'plasetry' anagrammed gives 'PSALTERY'.
(Other definitions for psaltery that I've seen before include "Ancient zither-like instrument" , "Dulcimer-like instrument" , "Obsolete stringed instrument" , "Old instrument like a dulcimer" , "Ancient plucked instrument" .)