Hilary sits next to 4 phonetic neighbors — Hillary, Hilary, and Ellery are the closest matches by sound. Most share Hilary's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"cheerful, merry, joyful"
"gift of God"
"mountain of strength"
"personal magnetism, compelling charm"
"crown, laurel"
"lake (from Welsh -lyn)"
"life, alive"
"wisdom, creativity (Celtic symbolism)"
"perfect, complete"
"heavenly"
"beloved by God"
"variant of Agnes/Vanessa"
"beam of light"
"pure"
"short form of Nicholas/Nicola"
"yellow, fair (light-haired)"
"mighty in battle"
"little, small"
"successful, one who attains her goals"
"noble serpent"
"crowned one, garland"
Similar sound: These names share phonetic patterns with Hilary — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin origins, giving them the same cultural heritage as Hilary.
Rhythm: Hilary is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.