Jump endlessly in meadow (3)
I believe the answer is:
lea
'meadow' is the definition.
(a lea is a grassy area)
'jump endlessly' is the wordplay.
'jump' becomes 'leap' (synonyms).
'endlessly' means to remove the last letter.
'leap' with its final letter removed is 'LEA'.
'in' is the link.
(Other definitions for lea that I've seen before include "Pasture, London river" , "area of grassland" , "authority for teachers" , "Grazing land" , "Meadowland" .)