auto-injectornoun [ C ]
also autoinjector /ˌɔː.təʊ.ɪnˈdʒek.tər//ˌɑː.t̬oʊ.ɪnˈdʒek.tɚ/a device used for injecting a single dose (= measured amount) of a drug into your own or another person's body:
If the autoinjector is pulled away from the skin before the injection is completed, a full dose may not be administered.