This is a common EC inclusive 1st person plural pronoun. It is preserved as such in Av.-Andian languages, in some archaic Darg. dialects (Chirag), Khinalug and most Lezghian languages. In PTs it has superseded the old exclusive pronoun *ži and has become the only 1st person plural. The same process must have occurred in PN (where there is no trace of *ži) - the morpheme *Lǟ > *lχō > *tχō became the only 1st person plural pronoun. Later, however, a new inclusive pronoun (*waj - originally from the 2d sing. *u_ō, "with you") was introduced in PN, and *tχō became, in its turn, exclusive. The paradigm of *Lǟ can be reconstructed as *Lǟ-(n) (dir. - cf. PL *Łä-n, Khin. ki-n, PN *tχō), *La- (dat. - cf. PL *Ła-, PN *tχa-), *ʔīL- (gen. - PL *-iŁ-) and *ʔēL- (erg. - PN *ʔāχu). The Av.-And. and Tsez. forms for the most part reflect the original ergative (and/or genitive) stem.
See Trubetzkoy 1922, 239; 1930, 273 (although there is hardly any connection with PAT *ħa- 'we').