Origins
The word 'herb' enters English in the late thirteenth century from Old French 'erbe' (grass, herb), from Latin 'herba' (grass, green crops, herb, plant, vegetation). The Latin word has no securely established PIE etymology, leading many linguists to suspect it is a pre-Indo-European substrate term — a word borrowed by Latin speakers from an earlier, non-Indo-European language of the Italian peninsula, perhaps related to the Etruscan or other pre-Roman Mediterranean cultures. This would make 'herb' one of the oldest surviving words in the English vocabulary, predating the Indo-European family itself.
Latin 'herba' had a broad semantic range encompassing grass, green crops, weeds, and useful plants alike. The specialization to 'plant used for flavoring or medicine' occurred gradually in the Romance languages and in English. In botanical Latin, 'herba' retains the broader sense: a herbaceous plant is any seed-bearing plant that does not develop persistent woody tissue — a definition that includes grasses, wildflowers, and crop plants alongside the culinary herbs.
The pronunciation of 'herb' famously divides the English-speaking world. American English preserves the silent h (/ɜːɹb/), reflecting the Old French form 'erbe,' which had lost the Latin initial /h/ — a regular sound change in the development from Latin to French. British English restored the /h/ in the nineteenth century by spelling pronunciation: seeing the letter h in the word, educated speakers began pronouncing it. This makes the American pronunciation paradoxically more historically faithful to the word's transmission through French, while the British pronunciation is a learned restoration based on the Latin spelling.
Latin Roots
The Latin derivatives of 'herba' have colonized scientific English. A 'herbivore' (Latin 'herba' + 'vorāre,' to devour) is a plant-eater. A 'herbicide' (herba + caedere, to cut, to kill) destroys plants. A 'herbarium' is a collection of preserved plant specimens. 'Herbaceous' describes non-woody plants. 'Herbal' designates both 'of or relating to herbs' and, as a noun, a book describing plants and their medicinal properties — the great herbals of the sixteenth and seventeenth centuries were foundational texts of European botany.
Spanish 'hierba' (also spelled 'yerba') from the same Latin source appears in 'yerba mate,' the South American caffeine-rich infusion made from the leaves of Ilex paraguariensis — literally 'mate herb.' The word 'mate' in this context comes from Quechua 'mati' (gourd, the vessel in which the drink was traditionally served).
The phrase 'herbal medicine' — using plants for therapeutic purposes — describes the oldest pharmaceutical tradition in human history, predating written records by millennia. The word 'herb' thus connects modern English speakers to practices that stretch back to the very beginnings of human culture, wrapped in a word that may itself predate the language family to which English belongs.