Trick old copper in outskirts of Hastings (5)
I believe the answer is:
hocus
'trick' is the definition.
(I've seen this before)
'old copper in outskirts of hastings' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'in' means one lot of letters goes inside another.
'outskirts of' says to hollow out the word (remove centre letters) (only letters on the outskirts).
'hastings' with its centre taken out is 'hs'.
'o'+'cu'='ocu'
'ocu' placed inside 'hs' is 'HOCUS'.
(Other definitions for hocus that I've seen before include "Deceive; stupefy with drugs or drink" , "Trickery" , "trick" , "Take in" , "Befuddle" .)