I just learned that the word safe is related to the word Greek word holo, as in hologram. Safe comes from the Norman French sauf, meaning "healthy" or "whole", which goes back to the Latin salvus, whence come words like salutary and salvation. This comes from the Proto-Indo-European form *solwo.
In Greek this became holo. The change from s to h was a regular thing in Greek; compare the Latin/Greek pairs sex and hex, sept and hept, semi and hemi. Holo simply meant "whole" or "entire" in Greek and apparently did not acquire the "healthy" senses as the Latin form did.
Semantic drift is always interesting, I think, because two related words can end up in such different and unpredictable places just by taking incremental steps away from each other.