Reconstruction:Proto-Sino-Tibetan/s-ni-s
Proto-Sino-Tibetan
    
    Etymology
    
- Proto-Sino-Tibetan: *s-nis (Chou, 1972); *sn̥jis (Coblin, 1986)
- Proto-Tibeto-Burman: *s-ni-s (Matisoff, STEDT); *s-nis (Benedict, 1972; Chou, 1972; LaPolla, 1987)
 
 
Apparently formed from the same root *ni(-s) as Proto-Sino-Tibetan *g/s-ni-s (“two”), showing the vestige of a quinary numeral system at some stage (probably much earlier than Proto-Sino-Tibetan), so that "7" was expressed as "5 + 2", as in Proto-Austronesian *pitu. However attempts to relate any part of this proto-form to the root for "five" (*l/b-ŋa) have been unsuccessful, and there is no evidence in other numerals (e.g. 6 and 1, or 8 and 3) to suggest the same quinary relationship.
Burmese has a prefix khu’ which as a separate morpheme means "unit, individual thing". Matisoff has argued that this component is cognate with *k(r)ut (“hand, arm”), the connection being via the five fingers used in counting. Tibetan བདུན (bdun, “seven”) is unrelated to this root and its etymology has been something of a mystery.
Preemption of the nasal root initial by prefix is seen in Chinese (if the Old Chinese reconstruction by Zhengzhang is valid) and Lolo-Burmese. Many Kuki-Chin-Naga languages have r-, ɣ- or g- as the root initial. Matisoff believes this resulted from "rhotacism", or liquefaction of the nasal.
Numeral
    
*s-ni-s
| Proto-Sino-Tibetan numerals | |
|---|---|
| ONE | *ʔit *kat *tjak ~ g-t(j)ik  | 
| TWO | *g/s-ni-s | 
| THREE | *g-sum | 
| FOUR | *b-ləj | 
| FIVE | *l/b-ŋa | 
| SIX | *d-k-ruk | 
| SEVEN | *s-ni-s | 
| EIGHT | *b-r-gjat ~ b-g-rjat | 
| NINE | *d/s-kəw | 
| TEN | *gip *ts(j)i(j) ~ tsjaj  | 
| TWENTY | *m-kul | 
| HUNDRED | *b-r-gja | 
| THOUSAND | *s-tawŋ | 
Descendants
    
- Old Chinese: 七 (*sn̥ʰid) /*sn̥id/ (Zhengzhang Shangfang); /*tsʰit/ (Baxter–Sagart)
- Middle Chinese: 七 (t͡sʰiɪt̚) /t͡sʰiɪt/
- Mandarin:
 - Cantonese:
 - Gan: /t͡ɕʰiʔ⁵/
 - Hakka:
- Sixian: 七 (chhit) /t͡ɕʰit̚²/
 
 - Huizhou: /t͡sʰiʔ²¹/, /t͡sʰi⁵/
 - Jin: /t͡ɕʰiəʔ²/, /t͡ɕʰiʌʔ¹³/, /t͡ɕʰiəʔ⁴³/
 - Northern Min:
- Jian'ou: 七 (chĭ) /t͡sʰi²⁴/
 
 - Eastern Min:
- Fuzhounese: 七 (chék) /t͡sʰɛiʔ²⁴/
 
 - Min Nan:
 - Xiang: /t͡sʰi²⁴/
 - Wu:
- Shanghainese: 七 (qiq4) /t͡ɕʰiɪ̆ʔ⁵⁵/
 
 - → Ai-Cham: sit⁷
 - → Japanese: 七 (shichi, shitsu)
 - → Korean: 칠 (chil)
 - → Proto-Tai: *cetᴰ (see there for further descendants)
 - → Vietnamese: thất
 
 
 - Middle Chinese: 七 (t͡sʰiɪt̚) /t͡sʰiɪt/
 - Proto-Tibeto-Burman:
 - → Proto-Karen: *Ɂnweᴬ, *Ɂnwetᴰ (Luangthongkum, 2013)
- S'gaw Karen: နွံ (nwee)