Origins
The English word 'bag' is a Scandinavian import. It entered Middle English as 'bagge' in the thirteenth century, almost certainly borrowed from Old Norse 'baggi,' meaning 'pack' or 'bundle.' The timing and geography of its appearance in English — concentrated in the northern and eastern dialects that were most heavily influenced by Norse settlement — confirm the Scandinavian origin. The word displaced or supplemented the native Old English 'poca' (pouch, pocket) and 'sæcc' (sack, from Latin 'saccus').
The deeper etymology of Old Norse 'baggi' is uncertain and much debated. The word has no clear cognates outside North Germanic: it appears in Swedish 'bagge' (a ram, and dialectally a bundle), Icelandic 'baggi' (a pack), and Norwegian 'bagge,' but it has no obvious West Germanic or East Germanic relatives. This distribution has led some scholars to suggest that 'baggi' is a pre-Germanic substrate word — borrowed into North Germanic from an unknown earlier language of Scandinavia, possibly pre-Indo-European. Others have tentatively connected it to a PIE root *bʰak- or *bʰag- relating to distribution or apportioning, but this remains speculative.
The word has been extraordinarily productive in English. 'Baggage' was borrowed from Old French 'bagage' in the fifteenth century — but the French word itself likely derived from the same Norse/Germanic source, making 'baggage' a round-trip borrowing (Norse > English/French > English). 'Bagpipe' (attested from the fourteenth century) is a straightforward compound: the bag is the animal-skin reservoir that the musician inflates and squeezes. 'Handbag,' 'sandbag,' 'beanbag,' 'airbag,' 'mailbag,' 'moneybag,' 'sleeping bag,' and 'teabag' are all transparent compounds that testify to the word's versatility.
Development
The cultural history of bags is as old as humanity itself. The earliest containers were almost certainly bags made from animal skins or woven plant fibers, predating pottery by tens of thousands of years. Otzi the Iceman (c. 3300 BCE), the naturally mummified man found in the Alps in 1991, carried several bags and pouches made from animal hide. In the medieval and early modern periods, bags served as the primary portable containers for travelers, merchants, and soldiers. The 'saddlebag' was essential to mounted travel; the 'moneybag' was the medieval banker's tool.
The figurative and slang uses of 'bag' in English are extensive. 'In the bag' (certain, secured) dates from the early twentieth century, possibly from game hunting (prey placed in the game bag). 'To let the cat out of the bag' (to reveal a secret) dates from the eighteenth century, supposedly referring to the fraudulent practice of selling a cat in a bag while claiming it was a piglet. 'To be left holding the bag' (to be stuck with blame or responsibility) is attested from the eighteenth century. 'Old bag' as a derogatory term for an older woman is nineteenth-century slang.
In modern usage, 'bag' has extended to contexts that Old Norse speakers could not have imagined. 'Airbag' (an inflatable car safety device) dates from the 1970s. 'Body bag' (a zippered container for transporting a corpse) entered common usage during the Vietnam War. In fashion, 'bag' has become a prestige category — the Birkin bag by Hermes, named after Jane Birkin, can sell for tens of thousands of dollars. In slang, 'that's my bag' (that's my interest or specialty) dates from 1960s jazz culture.
Legacy
The simplicity of the word — one syllable, three letters, a basic open-and-shut Germanic sound — belies its enormous utility. 'Bag' is one of those unpretentious workhorse words that English depends on daily, a Norse inheritance that has proven more durable than the leather and cloth containers it originally named.