ABC Game

line leader

last

new, never-ending

'pre' and 'post', past,

ready, rear, reveal

terminate, test balloon

vernal equinox, voluntary (in the musical sense)

are we stuck on x? Thanks to my trusty Webster's New Collegiate Dictionary (c 1977 LOL):

xerarch

Definition of xerarch. of an ecological succession. : developing in a dry place — compare hydrarch, mesarch.

zip, zero, zenith. (Good job on x, badger)

New category: 5 syllable words

Alphabetical

collaboration

Exhilarating

generosity

ignominious, indubitable

kleptomaniac, kleptomania, Kilimanjaro

laboratory

nationalism