The phrase "month that comes in like a lion and goes out like a lamb" refers to the month of March, which tends to have harsh, wintry weather at the beginning but becomes milder and more spring-like towards the end. Some synonyms for this phrase include "March winds and April showers bring forth May flowers," "winter's last gasp," and "the changing of the guard from winter to spring." Regardless of the wording, these phrases all capture the idea of a transitional period between seasons where nature is in flux and the weather can be unpredictable.