IPA: //ˌkoʊ.kənˈspɪr.ɪ.tər//
KK: /ˌkoʊkənˈspɪrɪtər/
A person who secretly helps another person to plan or commit a crime.
The police arrested the coconspirator along with the main suspect.
Coconspirator → It is formed from "co-" (meaning together) and "conspirator" (from Latin "conspirare", meaning to breathe together or plot together). The word refers to a person who plots or conspires together with others.
Think of people 'plotting together' — 'co-' means together, and 'conspirator' means someone who conspires.