This is the 1172nd most frequent Japanese word.
慣れ
Familiarity or habituation.
慣れる is used as a verb meaning 'to get used to' or 'acclimate'.
新しい環境に慣れるには時間がかかります。
It takes time to get used to a new environment.
慣れ is used as a noun indicating 'ease' or 'familiarity' in performing an action.
彼女のピアノ演奏にはプロのような慣れが見受けられます。
Her piano playing shows a professional level of ease.
慣れない uses the noun 慣れ with a negative form to describe something as 'unfamiliar'.