Alasdair sits next to 4 phonetic neighbors — Alistair, Alastair, and Alexander are the closest matches by sound. Most share Alasdair's Scottish cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"defender of men"
"priest"
"noble's settlement"
"powerful, mighty"
"world ruler"
"rocky settlement"
"slender, narrow"
"father, head of monastery"
"hospitable"
"my light, my flame"
"courteous, well-bred, polite"
"grey home, gravelly homestead"
"mighty hound, great wolf"
"oak tree, oak grove"
"Ireland, land of the west"
"son of Aodh (fire)"
"dark one"
Similar sound: These names share phonetic patterns with Alasdair — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Greek via Scottish Gaelic origins, giving them the same cultural heritage as Alasdair.
Rhythm: Alasdair is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.