Hadley sits next to 4 phonetic neighbors — Bradley, Radley, and Hartley are the closest matches by sound. Most share Hadley's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"from the heathland"
"blue crested bird"
"hare land, land of hares"
"great, kingly"
"from Devon, poet"
"possessing goodness; gift"
"God has shown favor"
"God is gracious (short form of Johannes)"
"thunder, god of thunder"
"initials, often James David or John David"
"lover of horses"
"short form of Cleopatra"
"cinnamon-like spice"
"surname of uncertain origin"
"possibly related to Old Norse Olaf (ancestor's relic)"
"one who moves smoothly"
"sacred covenant"
"modern invented variant"
"colt settlement; farm where young horses are kept"
"handsome, beautiful"
"placeholder birth name turned given name"
Similar sound: These names share phonetic patterns with Hadley — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old English origins, giving them the same cultural heritage as Hadley.
Rhythm: Hadley is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.