To remove the layer of scum from (a liquid etc.). / To remove (something) as scum. / To become covered with scum. / (obsolete) To scour (the land, sea etc.). / (obsolete) To gather together, as scum.

(sports) The act of spinning 540 degrees in the air, making 1½ turns.

The morphogenesis of astrogliomas

(physics) The line traveled by a particle beam in an accelerator