Coy about drink with Lieutenant, cunning (8)
I believe the answer is:
stealthy
'cunning' is the definition.
(thesaurus)
'coy about drink with lieutenant' is the wordplay.
'coy' becomes 'shy' (I've seen this before).
'about' means one lot of letters goes inside another.
'drink' becomes 'tea' (tea is a kind of drink**).
'with' says to put letters next to each other.
'lieutenant' becomes 'lt'.
'tea'+'lt'='tealt'
'shy' enclosing 'tealt' is 'STEALTHY'.
(Other definitions for stealthy that I've seen before include "That's Ely (anag.)" , "'Furtive, surreptitious (8)'" , "Covert - clandestine" , "Moving surreptitiously" , "'Sneaky, clandestine (8)'" .)