Definition of "flat" []

• Having a horizontal surface without a slope, tilt, or curvature. (adjective)
• Having a smooth, even, level surface: a skirt sewed with fine flat seams. (adjective)
• Having a relatively broad surface in relation to thickness or depth: a flat board. See Synonyms at level. (adjective)
• Stretched out or lying at full length along the ground; prone. (adjective)
• Free of qualification; absolute: a flat refusal. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "To summarize my previous comment, the LT data does not track surface temperature at all well – the LT temperature trend is essentially flat from ~1978 to ~1998, then there is the large 1998 El Nino spike and reversal, and then a ~0.2C step-up which has stayed ~flat for the most recent ~5 years."
• "Now if, _at the present moment_, this skein were cut with a straight knife at right angles to its length, the cut end would represent the _time plane_ -- that is, the present moment of all -- and it would be the same for all providing that the time plane were flat _But is it really flat_?"
• "V. i.112 (241,5) [as fat and fulsome] [W: flat] _Fat_ means _dull_; so we say a _fatheaded_ fellow; _fat_ likewise means _gross_, and is sometimes used for _obscene_; and _fat_ is more congruent to _fulsome_ than _flat_."