This is the 16062nd most frequent Polish word.
tęcza
Rainbow.
Here, 'tęcza' is used in its nominative singular form to denote the natural phenomenon of a rainbow.
Na niebie pojawiła się piękna tęcza.
A beautiful rainbow appeared in the sky.
In this sentence, 'tęczy' is in its genitive singular form, showing possession or belonging to the rainbow.
Kolory tęczy są niezwykle żywe.
The colors of the rainbow are incredibly vibrant.
In this case, 'tęczy' is again in its genitive singular form, indicating the origin of the colors used in painting.