独活(うど)の大木(たいぼく)good for nothing (of people), derived from a large 'udo' plant being of no use (only the young, tender, plant can be eaten)

独活(うど)の大木(たいぼく)のアイツは役(やく)に立(た)たない。

That guy is as useless as a large Udo tree. {good for nothing (of people), derived from a large 'udo' plant being of no use (only the young, tender, plant can be eaten)}

彼(かれ)は独活(うど)の大木(たいぼく)で、体(からだ)だけが大(おお)きいです。

He is like a large udo tree, good for nothing but his large physique. {good for nothing (of people), derived from a large 'udo' plant being of no use (only the young, tender, plant can be eaten)}

体(からだ)が大(おお)きいのに使(つか)い物(もの)にならない彼女(かのじょ)は独活(うど)の大木(たいぼく)だ。

Despite her large size, she is good for nothing, like a large, useless 'udo' plant. {good for nothing (of people), derived from a large 'udo' plant being of no use (only the young, tender, plant can be eaten)}

独活(うど)の大木(たいぼく)だと言(い)われないように僕(ぼく)はスキルを磨(みが)いています。

I am honing my skills so I won't be called a 'large udo plant', a term used for someone who is good for nothing. {good for nothing (of people), derived from a large 'udo' plant being of no use (only the young, tender, plant can be eaten)}

彼(かれ)は大(おお)きくて一見(いっけん)頼(たよ)りになりそうですが、実際(じっさい)はただの独活(うど)の大木(たいぼく)です。

He may look big and reliable at first glance, but in reality, he's just a good-for-nothing, like a large 'udo' plant. {good for nothing (of people), derived from a large 'udo' plant being of no use (only the young, tender, plant can be eaten)}