/flɛks/
[verb] To bend or tighten a muscle or joint; in modern slang, to show off your achievements, possessions, or abilities to impress others.
'Flex' started as a word for bending a knee but somehow became the internet's favourite way to describe showing off.
The story of 'flex' begins in ancient Rome, with the Latin verb 'flectere', meaning 'to bend' or 'to curve'. This root was extraordinarily productive in Latin — it gave rise to the past participle 'flexus', from which English eventually borrowed the word directly in the 16th century. At that time, 'flex' entered the language as a precise, almost clinical term: to flex something was simply to bend it, and the word was used mainly in anatomy and natural philosophy to describe the bending of limbs, tendons, and joints.
The Latin 'flectere' had already generated a rich family of descendants before 'flex' arrived in English. The same root, filtered through Old French 'flechir', gave English the word 'flinch' — originally meaning to bend away in fear. Meanwhile, the Latin form 'reflexus' (bent back) travelled through Medieval Latin and then into Middle French as 'réflexe', before arriving in English as 'reflex' in the 17th century. Another branch, Latin 'deflectere' (to bend away) → Old French 'deflectir' → English 'deflect', followed a similar path. Even 'flexible', meaning capable of bending, came directly from Latin 'flexibilis', itself from 'flectere'.
For centuries, 'flex' lived a quiet, technical life in English. Doctors told patients to flex their fingers. Scientists described how light could be made to flex around objects. Bodybuilders, once that culture emerged in the 20th century, adopted 'flex' as their own — to flex a muscle meant to contract and display it, usually to show its size and power. This physical, performative sense was crucial, because it planted a seed. Flexing a muscle was not just functional; it was a display intended to impress.
The leap from gym to slang happened gradually through African American Vernacular English (AAVE) in the late 20th century, where 'flex' began to mean showing off more broadly — flaunting wealth, style, or status. Hip-hop culture picked it up and amplified it dramatically. By the 1990s and early 2000s, artists were using 'flex' in lyrics to describe showing off jewellery, cars, or money. The word carried energy and swagger that no other term quite matched.
The internet and social media then did what they always do: they took a colourful piece of slang and spread it globally with astonishing speed. By the 2010s, 'flex' was everywhere online — used by teenagers in London, Lagos, and Los Angeles alike. New compound expressions formed almost overnight, most famously the phrase 'weird flex but okay', meaning 'that is a strange thing to boast about'. It is a remarkable journey: a Latin anatomical term for bending a joint had, after two thousand years, become one of the defining words of internet culture.