Another selection from the Iroha Karuta: I’ve found a site that has not just the Edo set, but the Kyoto and Osaka sets as well, so expect to see more of these as they catch my fancy.

鬼に金棒 (Oni ni kanabou; “[Like giving] a metal rod to an ogre”)

Definition:

Making something strong even stronger. An undefeatable strength. “Gilding the lily,” perhaps, although only in terms of increasing the power of some sort of already-formidable opponent or force.

from [http://www.irasutoya.com/2013/01/blog-post_870.html]

No verbs in this one. Just the two nouns 鬼 (oni) and 金棒 (kanabou), and the directional particle に (ni), generally rendered as “to.” Kanabou comprises two parts: 金, “metal/gold,” and 棒, “stick,” although it seems that the kanabou is a specific style of studded club, in use as far back as the Heian era.

Notes:

Kanabou can also be written as 鉄棒, literally “iron rod,” but neither the pronunciation nor the meaning changes.

A longer version of the saying supposedly continues, ~弁慶に薙刀 (~Benkei ni naginata), referencing the historical/mythical warrior-monk Benkei. This is idle speculation on my part, but I’d guess that the oni half of the phrase has, or originally had, a negative nuance, while the Benkei half had a positive one – and that together they made a complete set, so to speak. Don’t take my word for it, though. (That means you, Tim!)

An oni (variously translatable as “demon” or “devil,” “ogre,” etc.) is a mythical monster. Sometimes horned, often but not always inimical to humans, often portrayed as red- or blue-skinned, club-carrying (whence the kotowaza), and cannibalistic – although originally they were invisible spirits of misfortune. They play a role in the springtime festival of Setsubun.

Example sentence:

「今年、柔道部に参加しない？力が強いから、柔道で鍛えたら鬼に金棒だ。絶対大会で優勝できると思う」

(“Kotoshi, juudoubu ni sanka shinai? Chikara ga tsuyoi kara, juudou de kitaetara oni ni kanabou da. Zettai taikai de yuushou dekiru to omou.”)

[“Won’t you join the judo club this year? You’re strong, so if you train with judo it’ll make you unbeatable. I think you could definitely take first place at tournaments.”]