Definitions of flat:

• noun:   scenery consisting of a wooden frame covered with painted canvas; part of a stage setting
• noun:   a deflated pneumatic tire
• noun:   a shallow box in which seedlings are started
• noun:   a musical notation indicating one half step lower than the note named
• noun:   a level tract of land
• noun:   a suite of rooms usually on one floor of an apartment house
• noun:   freight car without permanent sides or roof
• adjective:   parallel to the ground

  Example: "A flat roof"

• adjective:   stretched out and lying at full length along the ground

  Example: "Found himself lying flat on the floor"

• adjective:   not made with leavening

  Example: "Most flat breads are made from unleavened dough"

• adjective:   lowered in pitch by one chromatic semitone

  Example: "B flat"

• adjective:   not increasing as the amount taxed increases
• adjective:   having lost effervescence

  Example: "Flat beer"

• adjective:   lacking variety in shading

  Example: "A flat unshaded painting"

• adjective:   not reflecting light; not glossy

  Example: "Flat wall paint"

• adjective:   (of a tire) completely or partially deflated
• adjective:   having no depth or thickness
• adjective:   having a horizontal surface in which no part is higher or lower than another

  Example: "A flat desk"

• adjective:   lacking contrast or shading between tones
• adjective:   without pleats
• adjective:   lacking stimulating characteristics; uninteresting

  Example: "A flat joke"

• adjective:   lacking taste or flavor or tang
• adjective:   flattened laterally along the whole length (e.g., certain leafstalks or flatfishes)
• adjective:   lacking the expected range or depth; not designed to give an illusion or depth

  Example: "A flat two-dimensional painting"

• adjective:   not modified or restricted by reservations

  Example: "A flat refusal"

• adverb:   wholly or completely

  Example: "He is flat broke"

• adverb:   at full length

  Example: "He fell flat on his face"

• adverb:   against a flat surface

  Example: "He lay flat on his back"

• adverb:   below the proper pitch

  Example: "She sang flat last night"

• adverb:   with flat sails

  Example: "Sail flat against the wind"

• adverb:   in a forthright manner; candidly or frankly

  Example: "Came out flat for less work and more pay"