flat

flat · adjective, adverb, noun, verb¹

1. Proto-Germanic*flataz
2. Old Norseflatr
3. Middle Englishflat
4. English todayflat

From Middle English flat, a borrowing from Old Norse flatr (compare Norwegian and Swedish flat, Danish flad), from Proto-Germanic *flataz, from Proto-Indo-European *pleth₂- (“flat”); akin to Saterland Frisian flot (“smooth”), German Flöz (“a geological layer”), Ancient Greek πλατύς (platús), Latvian plats, Sanskrit प्रथस् (prathas, “extension”). Doublet of plat and pleyt. The noun is from Middle English flat (“level piece of ground, flat edge of a weapon”), from the adjective. The algebraic sense was coined by Serre in a 1956 paper, originally as French plat.

flat · noun²

1. Proto-Indo-European · derived from*pleth₂-“flat”
2. Proto-Germanic · derived from*flataz“flat”
3. Proto-Germanic · inherited from*flatją“floor”
4. Proto-West Germanic · derived from*flati
5. Old English · derived fromflet
6. Middle English · derived fromflet“dwelling”
7. Scots · borrowed fromflet
8. English todayflat

From an alteration (due to Scots flatt (“a level part of a structure”)) of Scots flet, flett (“inner part of a house”), from Middle English flet (“dwelling”), from Old English flet, flett (“ground floor, dwelling”), from Proto-West Germanic *flati, from Proto-Germanic *flatją (“floor”), from Proto-Germanic *flataz (“flat”), from Proto-Indo-European *pleth₂- (“flat”). Akin to Old Frisian flet, flette (“dwelling, house”). More at flet, flat₁.

flat · verb³

1. Proto-Germanic · derived from*flatjaną“to make flat, flatten”
2. Frankish · derived from*flattjan“to move the palm of the hand”
3. Old French · derived fromflatir“to knock or strike down, dash”
4. Middle English · inherited fromflatten
5. English todayflat

From Middle English flatten, from Old French flatir (“to knock or strike down, dash”), from Frankish *flattjan (“to move the palm of the hand”), from Proto-Germanic *flatjaną (“to make flat, flatten”).

Words from the same roots