成 chéng is built on 戈 gē, the halberd. The dominant element is 戈, the ancient dagger-axe carried on a long shaft, and the early forms add a small marking stroke to it. The reading is one of a task brought to a finish: the weapon set down once the work of building, defending, or settling a thing is done. Where 戈 elsewhere signals cutting and warfare, here it is read as completion, the moment a labor reaches its full form and stands finished. The simplified and traditional shapes are identical, so the same glyph appears in both columns above.

From that core image of a thing brought to completion, several senses fan out:

1. To become, to turn into. One state finished and a new one standing in its place: 成为 chéngwéi (to become), 变成 biànchéng (to turn into).
2. To succeed, to accomplish. A labor carried through to its end: 成功 chénggōng (to succeed), 完成 wánchéng (to complete), 成就 chéngjiù (achievement).
3. Alright, that works. A colloquial yes that settles a matter on the spot: a bare 成 chéng meaning "fine, agreed, it works."
4. A tenth, ten percent. As a fraction word, 成 names one part in ten: 一成 yī chéng (ten percent), 九成 jiǔ chéng (ninety percent).
5. Ready-made, established, set. Already finished and fixed: 成语 chéngyǔ (a set idiom), 成绩 chéngjì (results, grades), 成熟 chéngshú (mature, ripe).

The thread through every sense is a process carried to its full conclusion. Whether the outcome is a new state, a won success, a settled agreement, a fixed fraction, or a finished and ripened form, 成 marks the point where becoming is done and the result stands complete.

The sense of 成 that learners meet most often is the one of carrying a task all the way through. 成功 chénggōng pairs 成 with 功 gōng (merit, the result of effort) to mean success, the labor brought to its rewarding end. 完成 wánchéng pairs 完 wán (whole, finished) with 成 to mean completion, the job done with nothing left over. And 成就 chéngjiù names the achievement itself, the lasting thing that effort produces.

Notice how often 成 sits in the second slot, where it acts almost like a result-marking ending: 做成 zuòchéng (to get something done), 写成 xiěchéng (to finish writing), 完成 wánchéng (to complete). In these the first character names the action and 成 reports that it reached completion. The same finishing 成 turns up in 达成 dáchéng (to reach, as in reaching an agreement), where what is finished is a meeting of minds.

A thing that has finished becoming is a thing that is ready, set, fully grown. From this sense 成 reaches into the language of results and ripeness. 成绩 chéngjì names the finished record of how one did, school grades or any measured outcome of effort. 成熟 chéngshú means mature or ripe, said of fruit on the branch, of a plan ready to act on, and of a person grown into steadiness.

The same fixed-and-finished 成 stands at the head of 成语 chéngyǔ, the set idioms of the language. A 成语 is a phrase already cast in a settled four-character form, ready-made and passed down whole, not assembled fresh each time. Here 成 means established rather than newly succeeded: the wording is finished and waits, complete, for use.

See the halberd, 戈, set down at the end of a day's labor: the wall is built, the work is defended, the task stands finished. That weapon resting over a completed job is the whole character. Everything 成 means is the moment a process reaches its full conclusion.

On a person, that finish is becoming, one self left behind and a new one standing whole (成为). On a labor, it is success, the effort carried through to its reward (成功). On a job, it is completion, nothing left undone (完成). On fruit or on character, it is ripeness, fully grown and ready (成熟). And on a phrase, it is the set idiom, cast once and handed down unchanged (成语). Whenever you meet 成, ask what has just been finished, and you will find the result standing complete.