Powder smuggled into eastern tattoo salon (4)
I believe the answer is:
soot
'powder' is the definition.
(I have seen 'Black powder ' mean 'soot' so perhaps 'powder' could also mean 'soot')
'smuggled into eastern tattoo salon' is the wordplay.
'eastern' shows that the letters should be reversed in order (letters written right to left or east to west).
'smuggled into' indicates a hidden word.
'toos' can be found hidden inside 'tattoo salon'.
'toos' reversed gives 'SOOT'.
(Other definitions for soot that I've seen before include "Smut" , "Chimney coating" , "Chimney deposit" , "Residue from burning" , "Deposited carbon" .)