two letters, one vowel
chaylanthes or cheelanthes, which is closer?
Neither. The letters are ei, whatever the vowel sounds like.
two letters, one vowel
These are the two competing guesses at the same syllable, one from people who hear it as ay and one from people who hear it as ee. The disagreement is real, and the first syllable of cheilanthes has been said all three ways in English. The spelling has never moved, because it is copying Greek letter for letter rather than recording anybody's pronunciation.
The class
One vowel sound that English can write several different ways.
Same name
Other spellings recorded for cheilanthes
The name