From Longman Dictionary of Contemporary Englishsea legsˈsea legs noun [plural] TTWthe ability to walk normally, not feel ill etc when you are travelling on a shipfind/get your sea legs I felt awful yesterday. But, thankfully, I’ve found my sea legs now.
Examples from the Corpus
sea legs• Men get sea legs and become catlike and grow beards.• It then dawned on them that maybe sea legs were required for the following morning.• At the end of the day was the guys from the heart of the city who found their sea legs and won.find/get your sea legs• At the end of the day was the guys from the heart of the city who found their sea legs and won. 