Spot some gypsies heading west (3)
I believe the answer is:
spy
'spot' is the definition.
(I know that spot can be written as spy)
'some gypsies heading west' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'heading west' shows that the letters should be reversed in order.
'yps' is hidden in the letters of 'gypsies'.
'yps' back-to-front is 'SPY'.
(Other definitions for spy that I've seen before include "Secret agent of government" , "One gathers information on enemies" , "Watch covertly like secret agent" , "Spot" , "Undercover agent" .)