Queen and King tucking into quiet drink (6)
I believe the answer is:
sherry
'drink' is the definition.
(I know that Sherry is a drink)
'queen and king tucking into quiet' is the wordplay.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'and' means one lot of letters go next to another.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'tucking into' means one lot of letters goes inside another.
'quiet' becomes 'shy' (both can mean timid or reserved).
'er'+'r'='err'
'err' put within 'shy' is 'SHERRY'.
(Other definitions for sherry that I've seen before include "Christmas drink?" , "Fortified 1 down [WINE]" , "Spanish fortified wine" , "booze" , "Jerez tipple" .)