What term refers to a hindrance or obstruction in doing something?

If something is bright or shining, especially in the dark, it is described as:

What does it mean to mark a gauge or instrument with a standard scale of readings?

To crouch down in fear is to:

Which word describes feelings of anxiety or dismay at something unexpected?

A slight involuntary grimace or shrinking movement in response to pain or distress is called:

To run or jump about playfully is to:

What word means to cause things to occur or operate at the same time or rate?

A loud and confused noise, especially from people shouting, is called: