burglar:
(plural: ‘burglars‘; pronunciation: the letter ‘u’ rhymes with the letter ‘u’ in “burn”, and the letter ‘g’ is said with a ‘g’ sound as in “gun” — for the right pronunciation, please click here)

a burglar at work, trying to break open a window
a thief who enters the buildings by breaking open the windows or doors (entering through windows of upper floors of the building) without making any noise, especially at night [also called ‘cat burglar’, and the act of stealing this way is called ‘burglary’];
a housebreaker,
There have been several incidents where a burglar breaks into a house and steals as many valuable as he/she can while the entire family is watching TV!
Some burglars are also expert ‘lock pickers’ who can break open any lock on any door of a building or a safe.
When there were no signs of damage to any furniture, doors or windows, the police came to the conclusion that the thief was an expert cat burglar.
