Style,
stigma,
stamen 
What is a flower?
This lizard, known for changing colors, does it partly to communicate with others of its kind
What is a chameleon?
After a few years inactive, the "Doomsday" one moved in a pessimistic direction in 2017
What is a clock?
The planets & Sun were thought to revolve around the Earth; in the 16th century, this Polish astronomer proved otherwise
Who is Copernicus?
The 600,000 of these that Americans travel over average 40+ years old & 1 in 9 is structurally deficient
What are bridges?
Hammer,
damper pedal,
keys 
What is a piano?
The Indonesian mimic type of this not only changes colors, it can impersonate other sea creatures
What is an octopus?
Term for anything transparent & rounded; the snow type is a popular souvenir
What is a globe?
A long-held notion was that a planet called this, like Spock's home, was between the Sun & Mercury; it was debunked
What is Vulcan?
The FAA lists airports as small, medium or large within this 3-letter designation that means you change planes there
What is a hub?
Keep,
parapet,
moat 
What is a castle?
The praying one gets a lot of press, but the dead leaf one sure lives up to its name
What is a mantis?
Arnold Schwarzenegger got this title nickname in a 1996 movie because he made people's pasts disappear
What is eraser?
Stress & a rich diet were blamed for this type of lesion in the stomach; turns out the culprit is the bacteria H. pylori
What is an ulcer?
Traffic & business can come to a halt when this pipeline with a primary name bursts beneath the road
What is water main?
Phone clamp,
extendable monopod, shutter button 
What is a selfie stick?
An incredibly poisonous type of stonefish is named for this coral structure with which it blends
What is reef?
Cliffs made of this form of soft, fine-grained white limestone rise on both sides of the Strait of Dover
What is chalk?
For hundreds of years, doctors treated disease by removing this, believing it balanced the body’s humors.
What is blood?
Solid waste is part of infrastructure; some is composted & some recycled, but most ends up in these places
What are landfills?
Envelope,
burner,
basket or gondola 
What is a hot air balloon?
Keep your eyes on the prize and name this flatfish, hatched with eyes like a regular fish that later move to one side of its head
What is a flounder?
A covert operation by one country's operatives pretending to be from another country is a "false" this attack
What is a false flag attack?
The 18th c. had the phlogiston theory of combustion; Lavoisier subbed in the theory of this newly discovered gas
What is oxygen?
Similar to dikes, these structures from the French for "raise" protect dry land from flooding
What are levees?