Fat babies regularly smudge clothes (7)
I believe the answer is:
blubber
'fat' is the definition.
(similar in meaning)
'babies regularly smudge clothes' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'smudge' becomes 'blur' (synonyms).
'clothes' is an insertion indicator (inserted letters are clothed in others).
The alternate letters of 'babies' are 'bbe'.
'bbe' going inside 'blur' is 'BLUBBER'.
(Other definitions for blubber that I've seen before include "Sob bitterly" , "Layer of fat under the skin of whales" , "Whale/seal fat" , "Fat of sea mammals - cry" , "Fatty tissue of a whale" .)