Časlav is a Slavic given name, which has several spelling variants: Časlav (Cyrillic: Часлав) in Serbian, Čáslav or Čéslav in Czech, and Czasław or Czesław in Polish.
In medieval Greek texts, the name is spelled as Τζασθλάβος.
The name consists of two elements, ča and slav.
The element ča is a Slavic root meaning "to await" or "to look forward to", expressing the idea that the child is an eagerly awaited gift.
The element slav is very common in Slavic anthroponyms.