[10] According to the hypothesis brought forward by Lithuanian historian Artūras Dubonis and linguist Simas Karaliūnas, the name of Lithuania (Lietuva) derived from leičiai.
The first mention of them in written sources is known from 1407, when Grand Duke Vytautas granted an estate and its staff, including leytey, to Manvydas, then an elder of Vilnius.
Their name was rendered in various forms: leythey, leyty, leytten, litten, лейти, лейци, лейтеве, лойти, людей лейтъскихъ, etc.
Leičiai, unlike villeins, owned their patrimonial plots, had the right to relocate and return, and were accountable for performing their duties as brethren and not as households.
[13] The synonymy of the words leičiai and Lietuva is shown by the historical naming of one place near Anykščiai in the times of the Grand Duchy of Lithuania.
Ten villages in Anykščiai volost was called Leičiai, Lietuva, also possibly Leituva: у Лейтахъ (1532; an example of Leičiai (as a place name) in writing); у войтовъстве Левътевскомъ (< Лейтевском; 1569), до Лейтовского рубежа (1545; possibly derived from Leituva); we … wojtowstwie Liejtowskim (1597); войтовъстве Летувъском (1595, 1597; derived from Lietuva or Lētuva).
A case of rendering Karšuva place name as w Korszewie, Korszewska, Korszewski powiat (16th century) shows that Левътевскомъ (< Лейтевском) could be reconstructed as Leituva.
John Steinkeller, who was a member of a council of Wrocław (Breslau), wrote in a letter addressed to his home town, that Sigismund, Holy Roman Emperor, was going to grant Vytautas the title of the King of Lithuanians: her wolde machen herczog Wytolten eynen konyng der Leytten.
For example, Lithuania is rendered as in writing as czwicshen Lythen und Prewssen (1415); as das land Litten with a further clarification that it was Aukštaitija in a narrative of a participant or witness of the Battle of Strėva.
In the same area there is Rukla town, maybe relating with the name Ruklys, son of King Mindaugas, and it is thought that leičiai could have lived in an estate now known as Perelozai located by Lietava.