Terror - Panic - Alarm - Fright
These are all words for the bad feeling you have when you are afraid.
Fear the bad feeling that you have when  you are in danger, when sth bad might happen, or when a particular thing  frightens you: (a) Fear of flying. | She showed no fear. 
  Terror a feeling of extreme fear: Her eyes were wild with terror.
  Panic a sudden feeling of great fear that  cannot be controlled and prevents you from thinking clearly: I had a sudden moment of panic. 
  Alarm fear or worry that sb feels when  sth dangerous or unpleasant might happen: The  doctor said there was no cause for alarm. 
  Fright a feeling of fear, usually sudden: She cried out in fright.
FEAR OR FRIGHT?
  Fright is a reaction to sth that has just  happened or is happening now. Use fear,  but not fright, to talk about things  that always frighten you and things that may happen in the future: I have a fright of spiders. | His fright of what might happen.
PATTERNS
  *a fear/terror of sth
  *in fear/terror/panic/alarm/fright
  *fear/terror/panic/alarm that...
  *to be filled with fear/terror/panic/alarm
  *a feeling of fear/terror/panic/alarm
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  Top Tips Abz Ingles   -   Notes on usage   -   Synonyms
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See also:
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