Siobhan sits next to 4 phonetic neighbors — Chevonne, Shevawn, and Shauna are the closest matches by sound. Most share Siobhan's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"God is gracious"
"dark-eyed one, hawk-eyed"
"pledged to God"
"white, fair, blessed"
"princess"
"one who is learned, a clerk"
"free one, Frenchman"
"bright, clear, famous"
"honey, sweet"
"youthful, downy-bearded"
"born in June; youthful"
"new star"
"grace, favored by God"
"ram"
"balance, temperament"
"courageous, spirited"
"dry, dry earth (flower etymology)"
"mercy (if from Eleanor)"
"variant of Mary, beloved"
"follower of Christ"
"devoted to the god of wine and festivity"
Similar sound: These names share phonetic patterns with Siobhan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Hebrew origins, giving them the same cultural heritage as Siobhan.
Rhythm: Siobhan is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.