Philonilla

This name is best known for being the name of saint Philonilla (also found written as Philonella), who lived in the first century AD. She was born into a Jewish family in Tarsus (located in what is now Turkey), which at the time was part of the Roman Empire, but had belonged to the Greeks not that long ago and as such was still heavily influenced by the Greek language and culture. Along with her sister Zenaida, saint Philonilla was a Christian physician who treated the sick for free, which made them the very first Holy Unmercenaries. This is what eventually caused them to become the first doctor-saints.

With all of this in mind, the saint's name is most likely a feminization of the masculine Greek name Philon, which was created by adding the Latin feminine diminutive suffix -illa to it (see names like Drusilla and Lucilla). Because of this, the variant Philonella is also encountered, because -ella is also a Latin feminine diminutive suffix (see names like Marcella). All in all, this name is essentially a Greco-Roman name. It is unlikely to be a full Greek name, as -illa and -ella are not suffixes that are found in the Greek language or at least native to it.