By a whisker
Definition 1 of 1
Pro Tip 1/3Visual Imagery
Think of the closeness of an actual whisker to something else to visualize how 'by a whisker' means very close. 
She avoided the accident by a whisker.
Pro Tip 2/3Emotional Intensity
This phrase often conveys a sense of relief or tension, emphasizing the closeness of an outcome. 
He passed the exam by a whisker and sighed in relief.
Pro Tip 3/3Informal Expression
'By a whisker' is informal and best used in casual conversation or writing, not formal contexts. 
I got the last ticket by a whisker!