be no slouch (at)

千葉の幕張インターナショナルスクールのMasuda Harukaさんがワシントンで行われたSpelling Contestで優勝しました。決勝での相手はSaji Yukaさんは"limburger," "liberalism," "pyromaniac" and "recalcitrant"などの難しい単語を正解してきました。slouchは通例否定文で「能無し」という意味，be no slouch (at)「〜が得意である」となります（『オーレックス英和辞典』旺文社）。これは口語でLDOCEではbe very good at somethingと定義されており，難解な単語を回答できたSajiさんの高い能力を表しています。（Sugiuchi）

Saji showed that she was no slouch by correctly spelling "limburger," "liberalism," "pyromaniac" and "recalcitrant" before going head to head with Masuda.
Settling for third to sixth place were Yuichi Yoshioka, 13, of Marist Brothers International School, the winner of last year's Japan Times Spelling Bee, Michaelynn Kopp, 11, of Matthew C. Perry Elementary School, Kathryn Codiamat, 9, of Stearley Heights Elementary School, and Gautham Elango, 10, of Tokyo YMCA International School.
http://www.japantimes.co.jp/text/nn20120311a4.html