Gilbert sits next to 4 phonetic neighbors — Albert, Elbert, and Hilbert are the closest matches by sound. Most share Gilbert's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"bright pledge, noble hostage"
"modern invented name, possibly 'sincere air' or 'great river'"
"flowing down (from Jordan)"
"great river, wide flowing water"
"guide, leader"
"victory of the people"
"descendant of Riagán"
"crooked enclosure"
"my God is help"
"western town, western settlement"
"noble elder"
"gift of God"
"the Nubian, dark-skinned"
"wealthy gift"
"modern invented name"
"Caesar, imperial leader"
"son of Carr, marshy land"
"soaring, high-flying"
"rock worker, craftsman"
"son of Harry"
"Yahweh has remembered"
Similar sound: These names share phonetic patterns with Gilbert — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Old German (Gisilbert) origins, giving them the same cultural heritage as Gilbert.
Rhythm: Gilbert is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.