IPA: /ˌsɪməlˈteɪniəsli/
KK: /sɪˌmʌl.tɪˈneɪ.əs.li/
Happening at the same time as something else.
The two events occurred simultaneously, making it difficult to choose which one to attend.
Simultaneously → It is formed from "simul" (meaning at the same time) and "-taneously" (derived from "taneous", from Latin "taneus", meaning pertaining to). The word "simultaneously" means occurring at the same time.
Think of 'simul' meaning 'at the same time' — that's why 'simultaneously' describes things happening together.