It formed from various dialects of the settlers and was shaped by the literary version of Polish language used in religious literature.

Since the 19th century, the subdialect began adopting loanwords from German, due to the Germanisation of the area.

[5] Typical of Masovian dialects, devoicing of word-final consonants before vowels and liquids is present here.

[6] The shift of initial ja-, ra- > je-, re- is present but limited to particular words: jek (jak), reno (rano).

Mobile -e- sometimes disappears in nouns formed with -ek, -ec, especially in the genitive of place names: podwieczórk (podwieczorek), do Mikołajk (do Mikołajek).

[6] Medial nasal vowels may raise: dziesiunti (dziesiąty), gorónce (gorące), gynsi (gęsi).

Similarly, eN may lower: ciamno (ciemno), as well as iN/yN: jenaczyj (inaczej), gościeniec (gościniec), and oN may raise: czerwónam (czerwonym).

Initial o- typically labializes to ô, as does u- to û- to a lesser extent.

[6] Soft labials decompose: wzino (wino), psiwo (piwo); around Olsztyn m’ shifts to mń: mniasto (miasto); but around Reszel to mn: mnasto (miasto); rarely to ń. f’, w’ may lose all labial elements: zidzioł (widział), przytrasiuło (przytrafiło), and the result sibilant can sometimes harden: psziwo (piwo), bżiały (biały); pszana (piana), bżały (biały).

św’, ćw’ i dźw’ harden: śwecie (świecie), ćwerć (ćwierć), dźwyrzów (drzwi).

kie, gie, ki, and gi sometimes harden: łokeć (łokieć), robaky (robaki), but generally are pronounced as in Standard Polish, with a soft pronunciation occurring more before kie than ki, but a hard pronunciation of gi.

Masculine and neuter nouns ending in sz, ż sometimes take -e instead of -u in the locative singular: o kosie (o koszu).

[6] Dual forms of pronouns are retained: łu noju (u nas), noma (nam), u woju (u was).

The first person plural imperative is typically -my of Standard Polish: choćmy (chodźmy); or sometimes the old dual ending -wa: chodziwa.