How to read the band →
Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Onyx
Onyx has been climbing in recent years. All-time it's been given to 8,632 U.S. babies, the 608th most common name by sound today, peaking at 1,271 in 2023, with 1,036 in 2025.
Onyx has no common alternate spellings by sound.
Rising
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).