What does bulb mean?
A bulb is a rounded underground storage organ produced by certain plants, most famously the onion, tulip, and daffodil. Structurally, it consists of a very short stem encircled by layers of thickened, fleshy leaves that store food and water, allowing the plant to survive dormancy and regrow vigorously each season. By extension, the word describes the familiar glass vessel housing a glowing filament in electric lighting, and more generally any rounded, bulb-like shape, such as the rubber end of a dropper or syringe. The term carries no strong connotation: it is equally at home in gardening manuals, physics lessons, and kitchen talk. Figuratively, phrases like 'the light bulb went off' capture a sudden flash of insight, giving this humble word a lively role in describing ideas as well as objects. Its blend of botanical precision and everyday familiarity makes it both practical and enduringly useful.
A rounded underground storage organ of a plant, consisting of a short stem enclosed by fleshy scale leaves, which sends up shoots and roots each growing season.
"Every October she buries tulip bulbs beneath the window box, counting on a blaze of colour come spring."
A glass enclosure containing a filament or gas that emits light when electricity passes through it.
"The room brightened instantly after he replaced the flickering bulb."
An expanded, rounded portion at the end of something, such as the rubber reservoir of a dropper or the base of a thermometer.
"Squeeze the rubber bulb gently to draw liquid into the pipette."
The plural follows the regular English pattern of adding -s; there are no irregular forms.
"The nursery sells spring-flowering bulbs in bulk during the autumn planting season."
The word 'bulb' comes straight from the ancient Greek for onion — and it's famously one of the hardest common English words to find a rhyme for.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bulb
The word 'bulb' entered English in the late sixteenth century, borrowed from French 'bulbe', which derives from Latin 'bulbus'. The Latin term itself traces back to the Greek 'bolbos', meaning an onion or similar rounded plant organ. This classical lineage reflects how central alliums were to ancient Mediterranean agriculture and cuisine, and the word has retained its core sense of a rounded underground plant part throughout its history in English.
Related word forms
How bulb is actually used
'Bulb' is neutral in register and common in both everyday speech and technical writing. In horticulture, it strictly denotes a layered storage organ like an onion's; corms and tubers are botanically distinct even though they are loosely called bulbs in casual use. The compound 'lightbulb' is often written as one word in American English and as two ('light bulb') in British English, though both forms are widely accepted.
Easily confused with bulb
'Blub' means to cry noisily, whereas 'bulb' refers to a plant organ or a rounded object such as a lamp.