#674 PTB *pʷam WOMB / PLACENTA / BELLY / STOMACH / NEST
The most general form of this complex word family is reconstructed as #163 PTB *s‑bʷa(m/p) SWELL / SWOLLEN / FAT / THICK / ROUNDED PART.
Like #1168 PTB *pʷu EGG / BIRD / ROUND OBJECT, some of the reflexes of *pʷam have initial w‑ #2108 PTB *wam, while others have an initial labial stop or derivative thereof #673 PTB *pam. All these forms meaning ‘womb / placenta / nest / belly’ clearly represent the same etymon as *p‑wam BELLY, presented separately as #137 PTB *pʷam. A further group of forms with nasal initials #3444 PTB *mam may also be brought into this word family. Finally, there is a strong likelihood that #680 PTB *s‑lam WOMB / PLACENTA is also allofamically related.
Some languages (e.g. Jingpho, Lashi, Zaiwa) show internal variation between stop and semivowel. The semantic association between WOMB and BELLY is too obvious to belabor. Belly was used frequently in early Mod. Eng. to mean WOMB: “As yet my wife hath not laid her belly” (Plumpton Correspondence 1549-50); “My belly did not blab, so I was still a Mayde” (William Warner, Albion’s England, 1592); “Why, she may plead her belly at worst” (John Gay, The Beggar’s Opera, 1728).1
Still another related form is #3 PTB *pum BODY / BELLY, found especially in Kuki-Chin, with a meaning which goes beyond the visceral / gastric area to cover the whole body.
Cf. also #2111 PTB *pwa(ŋ/n) BELLY / CENTER.