adj., adv., n., & v.
adj. (flatter, flattest) 1 a horizontally level (a flat roof). b even; smooth; unbroken; without projection or indentation (a flat stomach). c with a level surface and little depth; shallow (a flat cap; a flat heel). 2 unqualified; plain; downright (a flat refusal; a flat denial). 3 a dull; lifeless; monotonous (spoke in a flat tone). b without energy; dejected. 4 (of a fizzy drink) having lost its effervescence. 5 (of an accumulator, a battery, etc.) having exhausted its charge. 6 Mus. a below true or normal pitch (the violins are flat). b (of a key) having a flat or flats in the signature. c (as B, E , etc. flat) a semitone lower than B, E, etc. 7 Photog. lacking contrast. 8 a (of paint etc.) not glossy; matt. b (of a tint) uniform. 9 (of a tyre) punctured; deflated. 10 (of a market, prices, etc.) inactive; sluggish. 11 of or relating to flat-racing.
adv. 1 lying at full length; spread out, esp. on another surface (lay flat on the floor; the ladder was flat against the wall). 2 colloq. a completely, absolutely (turned it down flat; flat broke). b exactly (in five minutes flat). 3 Mus. below the true or normal pitch (always sings flat).
n. 1 the flat part of anything; something flat (the flat of the hand). 2 level ground, esp. a plain or swamp. 3 Mus. a a note lowered a semitone below natural pitch. b the sign (!!!) indicating this. 4 (as the flat) Brit. a flat racing. b the flat racing season. 5 Theatr. a flat section of scenery mounted on a frame. 6 esp. US colloq. a flat tyre. 7 sl. a foolish person.
v.tr. (flatted, flatting) 1 make flat, flatten (esp. in technical use). 2 US Mus. make (a note) flat. fall flat fail to live up to expectations; not win applause. flat arch Archit. an arch with a flat lower or inner curve. flat (or flat-bottomed) boat a boat with a flat bottom for transport in shallow water. flat-fish any marine fish of various families having an asymmetric appearance with both eyes on one side of a flattened body, including sole, turbot, plaice, etc. flat foot a foot with a less than normal arch. flat-four (of an engine) having four cylinders all horizontal, two on each side of the crankshaft. flat-head 1 any marine fish of the family Platycephalidae, having a flattened body with both eyes on the top side. 2 sl. a foolish person. flat-iron hist. an iron heated externally and used for pressing clothes etc. flat out 1 at top speed. 2 using all one's strength, energy, or resources. flat race a horse race over level ground, as opposed to a steeplechase or hurdles. flat-racing the racing of horses in flat races. flat rate a rate that is the same in all cases, not proportional. flat spin 1 Aeron. a nearly horizontal spin. 2 colloq. a state of agitation or panic. flat-top 1 US Aeron. sl. an aircraft-carrier. 2 sl. a man's short flat haircut. that's flat colloq. let there be no doubt about it. flatly adv. flatness n. flattish adj.
[ ME f. ON flatr f. Gmc ]