Western Lombard is a group of varieties of the Lombard language, a Romance language of the Gallo-Italic subgroup. It is spoken primarily in Italy and Switzerland. Within Italy, it is prevalent in the Lombard provinces of Milan, Monza and Brianza, Varese, Como, Lecco, Sondrio, and parts of Cremona (excluding Crema and its immediate surroundings), Lodi, and Pavia. In Piedmont, it is spoken in the provinces of Novara, Verbano-Cusio-Ossola, the eastern area of the Province of Alessandria (around Tortona), and a small part of Vercelli (Valsesia). In Switzerland, Western Lombard is spoken in the canton of Ticino and part of the canton of Graubünden.

Due to its historical association with the Duchy of Milan, Western Lombard is frequently referred to as Insubric (from Insubria and Insubres) or Milanese. The term Cisabduan ("Cisabduano", literally "on this side of the Adda River") is also used, particularly in linguistic contexts, following the terminology introduced by Clemente Merlo.

In Italian-speaking contexts, Western Lombard is often mistakenly described as a dialect of Italian.^{[citation needed]} However, Western Lombard and Standard Italian are distinct languages that are not mutually intelligible. While some speakers of different Lombard varieties may experience difficulties in understanding each other and might rely on a standard form for communication, varieties of Western Lombard are generally mutually intelligible. Western Lombard is considered relatively homogeneous compared to Eastern Lombard, although it exhibits some internal variations. These variations primarily involve differences in the pronunciation of the vowels /o/, /ɔ/, and the development of the affricate /ts/ into the fricative /s/.

Western Lombard lacks official status in Lombardy or any other region where it is spoken. Italian is the sole official language in Lombardy.

The following outlines the diachronic trends in Western Lombard plural declension, using Milanese orthography as a reference.

Most feminine nouns end in the inflection -a in the singular. The feminine plural form is typically non-inflected (e.g., singular la legora / plural i legor; singular la cadrega / plural i cadregh). The final vowel retains its original length, which is often long when followed by a voiced consonant and short when followed by a voiceless consonant. In certain cases, when the noun stem ends in specific consonant clusters, a final -i or a schwa may be inserted between consonants (for example, in Milanese: singular scendra, plural scendr > scender). For adjectives, the plural and masculine forms are frequently identical.

The majority of masculine nouns are uninflected, with the masculine plural always being non-inflected (e.g., singular el tramvaj / plural i tramvaj; singular el lett / plural i lett). When the noun stem concludes with particular consonant groups, both singular and plural forms may insert a schwa between consonants. Otherwise, a final -o (pronounced /u/) is added to singular nouns, and -i is added for plurals.

Masculine nouns ending in -in or, less commonly, -ett, form plurals in -itt (e.g., singular fiolin / plural fiolitt). Nouns ending in -ll have plurals in -j (e.g., singular el sidell / plural i sidej; singular el porscell / plural i porscej; singular el cavall / plural i cavaj). This pattern is also observed in the determinate article: singular ell > el, plural elli > ej > i.