noun
tempura soba without the noodles
A dish consisting of tempura and broth, served without the soba noodles. A playful reversal of たぬき (tanuki soba, which omits the tempura).
天ぬきは、天ぷらそばからそばを抜いたものです。
Ten-nuki is tempura soba with the noodles removed.
expression
missing the vital element
Idiomatic expression derived from the dish name, used when something is lacking its most important part. Often used humorously or critically.
この企画書、天ぬきだね。肝心の予算案が抜けてるよ。
This proposal is missing the vital part. The budget plan, the most important thing, is missing.
Tanuki soba is soba with tempura batter bits but no actual tempura, while ten-nuki is the opposite: tempura without the soba noodles.
From 天 (ten, short for 天ぷら tempura) + 抜き (nuki, removing). A wordplay on たぬき (tanuki soba), which omits the tempura; here the noodles are omitted instead.