set off (v.) Look up set off at Dictionary.com
verbal phrase; see set (v.) + off (adv.). From 1590s as "make prominent by contrast," 1610s as "adorn." Intransitive sense of "start on a journey" is from 1774. Meaning "separate from contect" (in typography) is from 1824; sense of "ignite, discharge, cause to explode" is from 1810.