This is the 17951st most frequent Polish word.
świętojańskim
"Świętojańskim" refers to something related to "Saint John's" (as in Saint John's Eve or festivities).
The word 'świętojańskim' is used as an adjective to describe the festival as related to Midsummer.
Zamierzamy uczestniczyć w świętojańskim festiwalu w tym roku.
We are planning to participate in the Midsummer festival this year.
Here, 'świętojańskim' is used as an adjective denoting the brilliance characteristically related to Midsummer.
Żar liści świętojańskim blaskiem rozświetlał gęstwinę drzew nocą.
The glow of leaves illuminated the thicket of trees with Midsummer brilliance during the night.
In this sentence, 'świętojańskim' serves as an adjective qualifying the time period as being connected to Midsummer.