Noun
1. A dark vertical line that appears on the abdomen during about three quarters of all pregnancies. The brownish streak is usually about a centimeter in width. The line runs vertically along the midline of the abdomen from the pubis to the umbilicus, but can also run from the pubis to the top of the abdomen. Linea nigra is due to increased melanocyte-stimulating hormone made by the placenta, which also causes melasma and darkened nipples. Fair-skinned women show this phenomenon less often than women with darker pigmentation. (wikipedia.org)
2. A dark vertical line running up the abdomen from the pubis to the navel that forms during pregnancy. (wiktionary.org)
3. A long narrow dark streak running along the midline of the abdomen, from the umbilicus to the pubis. (biology-online.org)
4. Linea alba that is hyperpigmented temporarily during pregnancy. (biology-online.org)
Word origin: Latin for “black line.”