set fire to (something)
To ignite something; to cause something to catch on fire. He set fire to the fireworks, then ran behind the car for cover. Police arrested the man on suspicion of setting fire to the local post office.
set fire to someone or something
and set someone or something on fireto ignite someone or something; to put someone or something to flames. The thief set fire to the building. The poor man accidentally set himself on fire.
set fire to
To cause to ignite and burn.