Stomach settler (7)
I believe the answer is:
antacid
'stomach settler' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for antacid that I've seen before include "Medicine to settle the stomach" , "Substance used to treat stomach upsert" , "Indigestion relief" , "Stomach drug" , "Indigestion remedy" .)