This is the 12924th most frequent Russian word.
лечебная
"Лечебная" means "medical" or "therapeutic" in English.
Here, "лечебной" is in the instrumental case modifying the feminine noun "атмосферой," meaning 'therapeutic' in relation to the resort's atmosphere.
Этот санаторий известен своей лечебной атмосферой.
This health resort is known for its therapeutic atmosphere.
Here, "лечебную" is an adjective describing the feminine noun "диету," indicating its purpose for recovery.
Врач порекомендовал лечебную диету для восстановления.
The doctor recommended a therapeutic diet for recovery.
In this sentence, "лечебная" as an adjective modifies the feminine noun "трава," indicating the herb's medicinal properties.