IPA: //ˌʌltrəˈsiːkrɪt//
KK: /ˈʌltrəˌsiːkrɪt/
Something that is extremely secret and not meant to be known by many people.
The government has an ultrasecret plan that only a few people are aware of.
Ultrasecret → It is formed from "ultra-" (meaning beyond or extreme) and "secret" (from Latin "secretus", meaning hidden or concealed). The word "ultrasecret" refers to something that is extremely hidden or confidential, beyond ordinary secrecy.
Think of something that is "beyond" ('ultra-') just being "hidden" ('secret') — that's why ultrasecret means extremely hidden.
No commonly confused words.