Definition of "phenocryst"

Some of the feldspar phenocrysts are more than 1 cm long, but most are less than 5 mm.

1965, Gordon A Macdonald and Takashi Katsura, Eruption of Lassen Peak, Cascade Range, California, in 1915: Example of Mixed Magmas, Geological Society of America Bulletin 76 (5), pages 475