The characters literally combine to mean “secretly cross Chencang.” The power of the idiom comes not from the literal words, but from the famous historical event they represent.
The idiom 暗度陈仓 (àn dù Chéncāng) is one of the most famous of the Thirty-Six Stratagems (三十六计, sān shí liù jì), a classic Chinese text on strategy. Its origin story is a cornerstone of Chinese historical lore. During the Chu-Han Contention (206–202 BC), the general Han Xin, serving the future emperor Liu Bang, was trapped. To attack the rival kingdom of Qin, he had to cross a mountain range. He ordered his men to make a great show of repairing the main plank roads (栈道, zhàndào) that had been destroyed, a massive and time-consuming task. The enemy general, Zhang Han, saw this and concentrated all his defenses there, laughing at the slow progress. This was the feint. While Zhang Han was distracted, Han Xin secretly marched his main army along an old, forgotten footpath through the Chencang pass, surprising and completely overwhelming the unprepared enemy forces. This story is often paired with its first half: 明修栈道 (míng xiū zhàndào) - “to openly repair the plank roads.” The full expression is 明修栈道，暗度陈仓 (míng xiū zhàndào, àn dù Chéncāng). A loose Western comparison might be a “red herring” or a “smokescreen.” However, those terms usually refer to a distraction meant to mislead or obscure something. 暗度陈仓 is more proactive; it's a complete strategic plan involving a feint and a decisive, secret offensive action. It embodies a cultural appreciation for clever, indirect strategy over brute force.
While its origins are military, the idiom is now used in many modern contexts, often with a slightly negative or sly connotation.
The connotation depends heavily on the context. In a historical or business discussion, it can be a neutral or even admiring term for a clever plan. In the context of relationships, it is almost always negative and implies betrayal.