What is a haberdasher?

Answer 1

There is a bit of variation in what a haberdasher is. Generally, a haberdasher is a men's outfitter or men's clothier. It may be that a haberdasher is someone who sells smaller articles and necessities or accessories for sewing, and these might include zippers, buttons and the like.

Answer 2

directly from wikipedia:

The word appears in Chaucer's Canterbury Tales. Haberdashers were initially pedlars, sellers of small wares, such as needles, buttons, etc. The word could derive from the Icelandic haprtask 'pedlars' wares' or the sack in which the pedlar carries them. In this sense, a haberdasher (Scandinavian name) would be very close to a mercer (French name). A haberdasher would retail smallwares, the goods of the pedlar, while a mercer would specialize in "linens, silks, fustian, worsted piece-goods and bedding".