This is the 16500th most frequent Polish word.
wieloletnich
"Of many years" or "long-standing."
Here, 'wieloletnich' describes the duration of commitment to international projects, indicating they last for multiple years.
Mój ojciec pracował w wieloletnich międzynarodowych projektach.
My father worked on long-term international projects.
In this sentence, 'wieloletnich' refers to plants that live and grow for multiple years.
Ogrody z wieloletnich roślin są bardziej ekologiczne.
Gardens with perennial plants are more ecological.
'Wieloletnich' here relates to friendships that have lasted for many years.