|1.||the ability to maintain one's balance on board ship, esp in rough weather|
|2.||the ability to resist seasickness, esp in rough weather|
To “have one's sea legs” is to be able to walk calmly and steadily on a tossing ship, or to become accustomed to a new or strange situation: “Even though Kimberly just joined the company, she's got her sea legs in a hurry.”
The ability to adjust to a new situation or difficult conditions, as in She's only spoken in public a few times; she hasn't found her sea legs yet. This expression was first recorded in 1712 and then referred to, as it still does, the ability to walk steadily on board ship, especially in rough seas. By the late 1800s it was being transferred to other challenging situations.