Pure; rejoice
Kaisy is a modern phonetic variant of Casey or a diminutive of Katherine. It likely draws its meaning from the Greek 'katharos' meaning pure, or the Latin 'rejoice' associated with the name Caia.
Less common today
Kaisy isn't in the latest US Top 1000. It last peaked at #9,480 in 2010.
US births per 5-year period, 1990βpresent (SSA data).