The name is of debated meanings, it is obviously composed of the Slavonic element slav meaning “glory” but the prefix of mieczy has always been a subject of debate.
Some theories that have interpreted the first element are:
- miecz from the Polish meaning “sword”
- mieć from the Polish verb meaning “to have.”
- miecić from the Polish verb meaning “to fling; to throw.”
The third is most likely, since Mieczysław is believed to be an erroneous corruption of the earlier Miecisław.
The designated name-day in Poland is January 1st.
Common diminutive forms are Miecio, Mieczyś, Mieteczek and Mietek.
Historically, the name was often anglicized to Mitchell by first generation Polish Americans. Mitchell has no etymological relation to Mieczysław other than sharing similar sonority.
Other, more archaic, Polish forms are Masław, Miecław, Miecisław, Miecysław and Miesław.
Other forms of the name include:
- Mečislav (Czech)
- Miecislas (French: very rare)
- Miecsiszláv/Miciszsláv (Hungarian)
- Menceslao (Italian: very rare)
- Mecislaus (Latin)
- Mecislavas/Mecislovas (Lithuanian)
- Mechyslav (Russian/Ukrainian)
A feminine forms are Masława and Mieczysława.