flap vs sag

flap

verb
  • To move (something broad and loose) up and down. 

  • To move loosely back and forth. 

  • Of a resource or network destination: to be advertised as being available and then unavailable (or available by different routes) in rapid succession. 

noun
  • A side fin of a ray. 

  • A consonant sound made by a single muscle contraction, such as the sound /ɾ/ in the standard American English pronunciation of body. 

  • The motion of anything broad and loose, or a sound or stroke made with it. 

  • Anything broad and flexible that hangs loose, or that is attached by one side or end and is easily moved. 

  • A piece of tissue incompletely detached from the body, as an intermediate stage of plastic surgery. 

  • A hinged leaf. 

  • The labia, the vulva. 

  • A hinged surface on the trailing edge of the wings of an aeroplane, used to increase lift and drag. 

  • A controversy, scandal, stir, or upset. 

sag

verb
  • To lean, give way, or settle from a vertical position. 

  • To cause to bend or give way; to load. 

  • To wear one's trousers so that their top is well below the waist. 

  • To pull down someone else's pants. 

  • To loiter in walking; to idle along; to drag or droop heavily. 

  • To sink, in the middle, by its weight or under applied pressure, below a horizontal line or plane. 

  • To lose firmness, elasticity, vigor, or a thriving state; to sink; to droop; to flag; to bend; to yield, as the mind or spirits, under the pressure of care, trouble, doubt, or the like; to be unsettled or unbalanced. 

noun
  • The state of sinking or bending; a droop. 

  • The difference in height or depth between the vertex and the rim of a curved surface, specifically used for optical elements such as a mirror or lens. 

  • The difference in elevation of a wire, cable, chain or rope suspended between two consecutive points. 

How often have the words flap and sag occurred in a corpus of books? (source: Google Ngram Viewer )