This is the 14752nd most frequent Polish word.
płynnymi
"Fluent" or "liquid" (instrumental plural form of "płynny").
Here, 'płynnymi' is used to describe substances (substancjami), indicating their liquid state.
Eksperymentowaliśmy z płynnymi substancjami w laboratorium.
We experimented with liquid substances in the laboratory.
The word 'płynnymi' is an instrumental plural form of the adjective 'płynny' (smooth/liquid) used to describe transitions (przejściami).
Rozmawialiśmy o płynnymi przejściami między tematami.
We talked about smooth transitions between topics.
In this sentence, 'płynnymi' describes movements (ruchami), emphasizing smoothness.