An initiator can refer to

• a device used to start the chain reaction in an atomic bomb of the Fat Man type.
• in polymer chemistry, a chemical compound that initiates a chemical chain reaction. Usually, it forms a free radical—an atom or molecule with at least one unpaired electron, or a group of atoms, charged or uncharged, that act as a single entity in reaction. (see radical (chemistry)).

• a SCSI initiator.

See also: explosive booster.

Polymers | Explosives | SCSI