Hungarian Historical Phonology ját
(dial.) ját 'Namensbruder'
First attestation/Old Hungarian data
[coming]
Important dialectal forms
lyát
lyátok
lëát
jád
(ÚMTSz: 1141, s.v. ját)
Uralic/Ugric/Pre-Hungarian reconstruction
Disputed:
UEW: PUg *jȣttɜ 'friend, fellow; Freund, Kamerad'
Status of the Ugric etymology
Implausible
Loan etymology
Hu dial. lyát ← Romanian leat ‘same age group (in the army)’ (Bakos MNy. 64: 72; WOT: 1232)
Hu ← Turkic *jat, cf. East Old Turkic āt ‘name’, Chuvash yat id. (criticized by WOT: 1232, reference to the initial suggestion missing)
Cognates suggested in earlier research
UEW:
Khanty: East (V) jö̆t 'mit', (Trj) jŏt
Mansi: South (TJ) jit, East (KU) jat, West (P) jät, North (So) jot
Commentary
Even though the word is listed among the plausible Ugric cognates in UEW, the etymology is completely irregular. UEW assumes that the front-vocalism in Ob-Ugric is due to influence from *j, but this is an ad hoc explanation that lacks parallels. The Ugric etymology is also considered implausible in WOT (1232).
UEW notes that the Hungarian word ját cannot be borrowed from Romanian leat (the Romanian origin of the Csángó dialect words leát 'egyidős', lyát 'egyidős, bajtárs' is accepted in the UEW) but it is in argued in WOT that ját is a secondary form that developed from dialectal lyát and that this was borrowed from Romanian.
The phonological side of the Turkic etymology is not discussed by WOT, as the Romanian loan etymology is considered better, but the problem seems to be that there is no evidence for a West Old Turkic reconstruction with word-initial *j-.
Conclusion
No Proto-Ugric word can be reconstructed.
References
UEW s.v. jȣttɜ: Proto-Ugric Uralonet