Pure
Kathren is a rare phonetic spelling variant of Katherine. It ultimately derives from the Greek name Aikaterine, which has been associated with the Greek word 'katharos' meaning pure since the early Christian era.
Less common today
Kathren isn't in the latest US Top 1000. It last peaked at #5,210 in 1991.
US births per 5-year period, 1990βpresent (SSA data).