To breathalyze someone is to make them breathe into a special machine so the police can see if there is too much alcohol on their breath to be allowed to drive. Officers breathalyze drivers at roadside stops or after a crash. It is a police and law word, not a kitchen-table one. The spelling breathalyze is the American one; British writing often has breathalyse. Though actually, the verb came after the machine's name: people had Breathalyzer first, then cut it down to make a verb. The test is of breath, not of blood; a blood test is a different, later step.