A calendar is nothing more than a system containing a list of days, weeks and months. So it is a way of measuring time. However, before the calendar we use today was created, the calendar time measurement system went through many changes and modifications. We are currently using the Gregorian calendar.
The calendar divides the year into shorter periods, of which a month is the superior unit. The Polish word miesiąc (month) has Pre-Slavic roots and it originally meant the moon. Interestingly, it is worth mentioning that in the past, the twelve-month period was referred to as lato, which was also the name of the season (summer). The word rok (year) is derived from the legal nomenclature and used to mean a term set by the court – usually it was a twelve-month period, hence today's understanding of the word. This also explains why the word rok in plural is lata – these are the so-called suppletions.
Names of months
Polish names of the months have a folk provenance and are closely related to the phenomena observed in nature, agricultural work, and the rhythm of rural life. They are at the same time the result of a special attitude towards time – experienced as cyclical and recurring. Almost all Polish month names are Slavic. The exceptions are March and May, which have a Latin provenance.
JANUARY – STYCZEŃ
In the case of styczeń, the origin of the name is not clear. The name of this month may be derived from the verb stykać się (to come into contact), because it is the place where the old and new year meet. It is also assumed that the first month of the year owes its name to the noun tyki – these are wooden rods acquired by farmers at the beginning of the year.
FEBRUARY – LUTY
The adjective luty in Old Polish meant severe/sharp and hence the name of the second month of the year – after all, in February there is usually a heavy frost. The second month of the year had also other names in the past. It was called gromnicznik (because of the feast of Our Lady of Thunder candles – Matki Boskiej Gromnicznej, celebrated on February 2) and mięsopustnik (from the word mięsopust – the end of carnival / beginning of Lent).
MARCH – MARZEC
Some people suppose that the word marzec comes from the verb marznąć (to freeze), but this is not true. Although there are still frequent frosts in March, its name is undoubtedly derived from the Latin – it derives from the adjective martius, which means “dedicated to Mars, god of war”.
APRIL – KWIECIEŃ
The name kwiecień leaves little doubt and the explanation of its origin is extremely simple. After all, many trees and flowers bloom (kwitnie) in April.
MAY – MAJ
The name of the fifth month of the year is another gift from Latin – it comes from the name of the Roman goddess Maia.
JUNE – CZERWIEC
The name czerwiec comes from czerw (bee brood), i.e. the larvae of bees that hatch at that time of year, or from czerwiec polski (Polish cochineal), a species of small insects whose larvae were harvested in that part of the year in order to obtain a valuable dye used for colouring fabrics red.
JULY – LIPIEC
In the case of lipiec, it is very simple – the name comes from the lime trees (lipy) blooming at this time of year. Hence the other names of the seventh month, such as lipień or lipnik.
AUGUST – SIERPIEŃ
August took its name from the sickles (sierpy) which were used to reap the grain at that time – sickles were a common and basic tool during harvesting. It was also sometimes referred to as stojaczek or stojęczeń, which was related to the standing (stojąca) position taken by the reapers.
SEPTEMBER – WRZESIEŃ
September is the month when heather (wrzos) blooms, so... everything is clear.
OCTOBER – PAŹDZIERNIK
October owes its name to the processing of flax and hemp, which was intensively worked on at that time, namely to shives (paździerze), i.e. dry stems, which are parts of the fibre that fell off during processing. Sometimes you can also find the term winnik, derived from winobranie (grape harvesting).
NOVEMBER – LISTOPAD
The name listopad is very pictorial and comes from falling leaves (spadające liście).
DECEMBER – GRUDZIEŃ
The name grudzień relates to frozen clods (grudy) of earth. The last month of the year was also referred to as jadwent (in reference to the liturgical calendar – jadwent comes from the word adwent, meaning Advent, which usually starts in December), godnik (Gody means Christmas) or prosień (from the sun's rays – promienie reflected in the snow – śnieg).
Source: pl.wikipedia.org; polszczyzna