fluency
US /ˈfluː.ən.si/
UK /ˈfluː.ən.si/

1.
the ability to speak or write a particular foreign language easily and accurately
:
•
Her fluency in French impressed everyone.
•
He achieved near-native fluency after living abroad for years.
2.
the quality of being able to move or flow smoothly and easily
:
•
The fluency of the dancer's movements was captivating.
•
The architect designed the building with a remarkable fluency of lines.