Shannon sits next to 4 phonetic neighbors — Shanon, Brennan, and Cannon are the closest matches by sound. Most share Shannon's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"old river, ancient waters"
"free man"
"ridge of rock or coral beneath the sea"
"sheltered bay, cove"
"beloved of God, beloved of Yahweh"
"belonging to Christ"
"lord, ruler"
"divine, godlike (Sanskrit)"
"son of Rhys, ardor and enthusiasm"
"short form of Trevor meaning large homestead"
"departure, going out"
"powerful, warrior"
"son of Lars (son of Lawrence)"
"leopard, swift and fierce"
"from Wynstan's estate"
"trout (from the fish's spotted pattern)"
"invented American name, possibly river (from Zaire)"
"lover of the earth"
"bright, shining"
"hollow, empty space"
Similar sound: These names share phonetic patterns with Shannon — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Irish Gaelic origins, giving them the same cultural heritage as Shannon.
Rhythm: Shannon is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.