/buːn/
[noun] A thing that is very helpful or brings a great advantage; a welcome benefit or gift. It can also mean a favour that someone asks for.
The word 'boon' originally meant a prayer — people once had to beg the gods before it became a simple gift.
The word 'boon' has two distinct histories that have quietly merged in modern English, which makes it more interesting than it first appears. The older of the two threads stretches back to Old Norse 'bón', meaning a prayer, a petition, or a request. This word was carried into northern England and Scotland by Viking settlers during the 9th and 10th centuries, and it entered Middle English as 'bone', meaning a favour asked of someone — particularly a great lord or a deity. When you asked for a 'boon', you were not receiving a gift freely given; you were humbly making a request, almost like a prayer.
This sense of petition and prayer connects 'boon' to a very ancient family of words rooted in the Proto-Indo-European base *bha-, meaning 'to speak' or 'to say'. From this root, Old Norse developed 'bón' (prayer), and Old English developed 'gebed' (prayer, now 'bead' — because prayer beads were counted while praying). The idea of speaking a desire aloud to someone more powerful than yourself is baked into the word's very origins.
Over time, the meaning drifted in a natural and human direction. If you successfully asked for a favour and received it, the word gradually came to describe the thing received rather than the act of asking. By the 14th and 15th centuries, 'boon' had shifted from meaning 'a request made' to 'a gift or benefit granted'. This kind of meaning shift — from the action to the result — is extremely common in English, and it gave 'boon' the sense we use most often today: something beneficial and welcome, a stroke of good fortune.
The second thread involves a separate Old French word, 'bon', meaning 'good', which came from Latin 'bonus' (good). This word flooded into English after the Norman Conquest of 1066, and over the centuries it blended with the older Norse sense of 'boon', reinforcing the positive, pleasant flavour of the word. Latin 'bonus' also gave English words like 'bonny' (via Scottish and Northern English dialects), 'bonus' itself, 'bounty' (via Old French 'bonté' → Middle English 'bounte'), and even 'bonanza' (via Spanish). These cousins all carry that same glow of goodness and generosity.
The phrase 'boon companion' is a lovely fossil of the French influence — here 'boon' works as an adjective meaning 'good' or 'jolly', directly from Old French 'bon'. So a 'boon companion' is a good and merry friend, someone whose company is a pleasure. This adjectival use has almost disappeared from modern English, but it survives in this fixed phrase and reminds us that 'boon' once did double duty as both noun and adjective. Today, the noun form dominates, and we most often use it to describe things — a new medicine, a piece of technology, a stroke of luck — that arrive in our lives like an answered prayer, which is, fittingly, exactly what the word once meant.