Terrible lie about introduction to Scarborough Fair? (4)
I believe the answer is:
isle
'fair?' is the definition.
(Fair Isle is a Scottish island)
'terrible lie about introduction to scarborough' is the wordplay.
'terrible' indicates an anagram.
'about' means one lot of letters goes inside another.
'introduction to' says to take the initial letters.
The first letter of 'scarborough' is 's'.
'lie' anagrammed gives 'ile'.
'ile' going around 's' is 'ISLE'.
(Other definitions for isle that I've seen before include "one has water all round" , "This could be key" , "eg Man, Ely" , "I shall hear" , "Land encircled by water" .)