fear

an unpleasant emotion caused by the belief that someone or something is dangerous, likely to cause pain, or a threat

ORIGIN Old English [calamity, danger,] [frighten,] also [revere.]

terror

extreme fear : people fled in terror | [in sing. ] a terror of darkness.

• the use of such fear to intimidate people, esp. for political reasons : weapons of terror.

• [in sing. ] a person or thing that causes extreme fear

ORIGIN late Middle English : from Old French terrour, from Latin terror, from terrere ‘frighten.’