In Britain and Australia, a haberdasher is a dealer in dressmaking and sewing goods; in North America, he’s a dealer in men’s clothing.
One of my American dictionaries, in making clear the ways in which this word is used in different places, uses two words that sound mildly odd in Britain. In the USA, it says, a haberdasher sells men’s furnishings (such as shirts, ties, gloves, socks, and hats); in the UK, he or she sells small wares and notions (such as buttons, needles, ribbons, and thread).
This substantial divergence in sense reflects the muddled history of this odd-looking word, which in origin has nothing whatever to do with anybody dashing anywhere. It may come from an Anglo-Norman French word hapertas, which may have been a type of fabric. But nothing other than these vague suppositions is known about its origin. It went through lots of variant spellings before it settled down to the modern form around the middle of the sixteenth century.
Its meaning down the centuries has been as diverse as its origin is mysterious. When it appeared, in the thirteenth century, it meant a trader in a range of goods. According to early chroniclers, these included: “glasses, daggers, swerdes [swords]”, “mousetrappes, bird cages, shooing hornes, lanthornes, and Jews trumpes [Jew’s harps]”, and “bookes, pictures, beades, crucifixes” — what we would now think of as the stock of an eclectic general store.
Around the sixteenth century, the trade narrowed in focus and often referred to a hatter, a sense now obsolete (such sellers were also called milliners, originally a trader in goods from Milan, a term now restricted to providers of female headgear). Another part of the trade split off, that of providing a multitude of small items needed by tailors and dressmakers, the notions of that dictionary reference.
By some curiosity of cultural and linguistic history not fully understood the term has come to have different senses in Britain and North America.