Hence appearing in 'Mother Goose' (4)
I believe the answer is:
ergo
'hence' is the definition.
(I've seen this before)
'in mother goose' is the wordplay.
'in' indicates a hidden word.
'ERGO' is hidden in the letters of 'mother goose'.
'appearing' acts as a link.
(Other definitions for ergo that I've seen before include "Thus" , "It follows" , "so philosopher wrote in Latin" , "Therefore - what a goer" , "Therefore (Latin)" .)