Like “liberal,” “retro” and “post-modern,” “riot grrrl” is a term co-opted in such sardonic spirit that its adherents shy from the label. But a dozen years ago, those angry, angry women of Olympia, Wash., endeavored to storm the punk rock boy’s club on behalf of young impressionable girls everywhere. For a few years they howled (Hole), stomped (Bikini Kill), and hurled their used tampons (Silverfish) from stages across America. Finally, the movement collapsed under the weight of political pretension and media overexposure, and the riot grrrls fossilized into footnotes to grunge.

Sleater-Kinney, who debuted in 1995 just as the riot quieted, was the Pacific Northwest girl-band who transcended this trajectory, meeting increased critical and popular acclaim with each album. On its sixth effort, “One Beat,” the group has streamlined, stretched and enriched its sound yet further. The songs are surprisingly catchy, sprightly and blithe. Through lustrous vocal harmonies and luscious guitar textures, Sleater-Kinney has crafted an illusion of effortlessness without slowing their punk rock pulse or selling their riot grrrl soul.

With “One Beat,” the trio has outgrown their old safe formulas: the crunchy, clunky punk of “Dig Me Out” and the cute, cloying pop of “All Hands on the Bad One.” The only novelty single here is “Combat Rock,” an anti-Bush anthem with lukewarm lyrics that rocks hard but ages fast. On more graceful tracks like “The Remainder” and “O2,” Sleater-Kinney achieves sophistication without complication, precision without overproduction, and energy without excess.

“One Beat” also provides definitive evidence that Sleater-Kinney’s main comparative advantage — separating it from the paleo-punk clones, ’60s garage revivalists, and various bands with hyphens and numbers in their names that have walked the well-worn path from punk to popularity — boils down to two factors. The first and most obvious is that Sleater-Kinney doesn’t drone, moan, croon, rap or growl. Instead, all three members sing with a cohesive quicksilver harmony. Sleater-Kinney’s main appeal still lies in the elegant, elastic balance of Corin Tucker’s spastic, scream-sung alto against the sweet, mellow background harmonies of Carrie Brownstein and Janet Weiss. These vocals cover Sleater-Kinney’s most serious flaw — lackluster lyrics (which consistently attack Ivy League men, for some mysterious reason).

The second factor is craftsmanship (excuse me, craftsgrrrlship). A generous helping of thought and sweat underlies the veil of spontaneity in “One Beat.” Janet Weiss’ firecracker beats tightly counterbalance Brownstein and Tucker’s ever-interweaving guitars. Songs like “One Beat” and “Oh” show guitar and vocal melodies breaking against asymmetric rhythms in waves that would sound off-kilter if they weren’t so carefully, complexly on-kilter.

After their last album, the Beach-Boys-slick “All Hands on the Bad One,” Sleater-Kinney left open the possibility of permanently jettisoning their Olympian riot grrrl roots. “One Beat” slams this door and shows Sleater-Kinney freed from their own insecurities, ready again to play hard, fast, tight rock.