1. A short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead
   - protoactinium, Pa, atomic number 91

Derived forms: protactiniums

Type of: metal, metallic element

Encyclopedia: Protactinium

• butterfly orchid
• butterfly orchis
• butterfly pea
• butterfly plant
• butterfly ray
• butterfly stroke
• butterfly valve
• butterfly weed
• butterfly-shaped
• butterflyfish
• butterhead lettuce
• buttermilk
• buttermilk biscuit
• buttermilk pancake
• butternut
• butternut squash
• butternut tree
• butterscotch
• butterweed
• butterwort
• buttery
• butthead
• buttie
• buttinsky
• buttle