Edge one may observe in the Mendips (3)
I believe the answer is:
hem
'edge' is the definition.
(I know that hem is a type of edge)
'one may observe in the mendips' is the wordplay.
'one may observe in' indicates the answer is hidden within the clue (the answer can be observed in the clue).
'HEM' is hidden in the letters of 'the mendips'.
(Other definitions for hem that I've seen before include "try to attract attention" , "Part of skirt" , "Double-backed border of a garment" , "A stitched border of cloth" , "may attract attention" .)