Real Dictionary

morning sickness
uncountable noun: If a pregnant woman has morning sickness, she feels sick or is sick, often in the morning.

morning sickness in American English
a condition of nausea and vomiting, sometimes accompanied by dizziness, headache, etc., that affects many women during the first months of pregnancy: it occurs most often in the morning
noun: nausea occurring in the early part of the day, esp. as a characteristic symptom in the first months of pregnancy

morning sickness in British English
noun: nausea occurring shortly after rising: an early symptom of pregnancy