1) In its earliest history this was used of a long stuffed pillow or cushion but it soon acquired meanings related to padding or support.
In the cutlers’ vocabulary it was the projecting ‘shoulder’ of a knife, where the blade is inserted into the handle, one of the three metal parts, that is blade, bolster and tang. It is found in one of the trade’s first by-laws, two centuries before other noted references: 1625 No gold or silver to be put on the blades, bolsters or hafts of any knives except such as be worth or sold for five shillings the dozen on pain of 20s. In 1701, Henry Heward had a Stithy Stock cow trough bolster stythy valued at ten shillings. It was also used in connection with church bells, possibly a pad of some sort designed to prevent friction: 1596 for mending 2 belltiers & making 3 boulsters & 4 cottrells, Howden. More generally, and from an early date, it accompanies ‘feather-bed’ in wills and inventories: 1430 alium lectum ... cum fethirbed et bolstyr, Ripon. Both words are used of cushiony moorland terrain, as in Bolster Moor and Featherbed Moss.