Does the term "novel attack" resonate with security teams? or does "unknown attack" resonate better? What would you consider novel/unknown attacks? Does your current threat detection solution detect novel/unknown attacks?

Novel attack resonates more. These attacks may include multiple stages and exploit vulnerabilities to perform an EDR bypass, C2, or ransomware. 

I always think of 0-day vulns and associated attacks as novel.

Novel attack certainly resonates more. Unknown attacks are only unknown until forensics figure it out.  A robust incident detection and response system (SIEM, UEBA, XDR) should be able to detect unusual activity and let your SOC investigate. them.