bone marrow

noun

: a soft highly vascular modified connective tissue that occupies the cavities of most bones and occurs in two forms:

a

: one that is yellowish, consists chiefly of fat cells, and is found especially in the cavities of long bones

b

: one that is reddish, is the chief site of blood cell formation, and occurs in the normal adult in cancellous tissue especially of certain flat bones

called also red marrow

Examples of bone marrow in a Sentence

Recent Examples on the Web

It is stored in an inactive form in cells such as the liver, spleen, bone marrow, and immune system—acting as the body’s reserve bank, indicating how much iron is available for future use. — Tatiana Dias, Vogue, 30 June 2026

After going to the doctor for blood tests, he was eventually diagnosed with bone marrow cancer. — Lexi Lane, PEOPLE, 28 June 2026

Tests showed abnormalities in her urine and bone marrow, leading to a diagnosis of multiple myeloma, a form of blood cancer than can cause kidney problems. — Kerry Breen, CBS News, 27 June 2026

Blood stem cells can be collected through a blood draw — which accounts for 90% of donations — or surgery to gather bone marrow, according to the donor organization. — Rylan Digiacomo-Rapp, The Orlando Sentinel, 27 June 2026

Word History

First Known Use

1590, in the meaning defined above

Rhymes for bone marrow

• caballero
• mescalero
• aero
• faro
• garo
• narrow
• pharaoh
• sparrow
• taro
• bolero
• bracero
• estero

Kids Definition

bone marrow

noun

: a soft tissue rich in blood vessels that fills the cavities of most bones and occurs in two forms:

a

: one that is yellowish and fatty and is found especially in long bones (as the femur)

b

: one that is reddish, is the main place where blood cells are formed, and in adults is limited especially to certain flat or short bones (as the ribs)

Medical Definition

bone marrow

noun

: a soft highly vascular modified connective tissue that occupies the cavities and cancellous part of most bones and occurs in two forms:

a

: a whitish or yellowish bone marrow that consists chiefly of fat cells and is found especially in the cavities of the long bones

called also yellow marrow

b

: a reddish bone marrow that contains little fat, is the chief site of red blood cell and blood granulocyte formation, and occurs in the normal adult in cancellous tissue especially of certain flat bones

called also red marrow