Meanings for Leafeon (when leafeons say that):any word that is 7 letters or longer.
Meanings for leaf, feon, afeo, eafe (when leafeons say that): any word with 4, 5, or 6 letters.
Meanings for eon, lea (when leafeons say that): any word with 3 letters in it.
Meanings for le, on (when leafeons say that): any word with 2 or less letters in it.

How can you tell
You can tell by there voice like any other pokèmon
Like if a Leafeon said
Le eon
In an angry voice it means go away.