This is the 7729th most frequent Polish word.
majówkowy
Related to May or May festivities.
The word *majówkowy* is used here as an adjective describing the mood associated with celebrations during May holidays.
Majówkowy nastrój udzielił się wszystkim w pracy.
The festive mood of the May holiday spread to everyone at work.
*Majówkowych* in this sentence describes the memories related to activities or trips taken during the May holiday period.
Mam sporo majówkowych wspomnień z rodzinnych wypadów.
I have many memories from family trips during May holidays.
Here, *majówkowy* modifies 'piknik,' indicating that the picnic is organized to celebrate or coincide with the May holiday.