(physics) Any of three semistable mesons, having positive, negative or neutral charge, composed of up and down quarks/antiquarks.

(nonce word) A word of disputed meaning; perhaps, abounding in marsh marigolds.

plural of pion

(physics, of a theory) That includes pions

A theoretical type of antimatter rocket which uses proton-antiproton fuel, and magnetic rocket funnels to direct the π-on exhaust. The pi meson particles are created by the matter-antimatter annihilation of protons and antiprotons.

plural of pion rocket

(neurology) An axon that lays down the initial growing path for the other axons of the same neuron to follow.

Involving accomplishments or activities that have not been done before, or developing or using new methods or techniques.

The activity of the verb pioneer. / A scoutcraft skill that involves building structures using staves and knots.

present participle of pioneer