IPA: /ˌɪnkəˈmjunɪkəbli/
KK: /ɪnˌkəˈmjunɪkəbli/
In a way that cannot be communicated or expressed clearly.
He felt incommunicably lost in the conversation, unable to share his thoughts.
Incommunicably → It is formed from "in-" (meaning not), "communicable" (from Latin "communicare", meaning to share or make common), and "-ly" (meaning in a manner). The word describes a manner of being unable to share or communicate.
Think of 'not' ('in-') being able to 'share' ('communicare') something — that's why incommunicably means unable to communicate.