无【wú】

无 means "have no" or "there is no" in written Chinese, the formal 没有. It takes a noun straight after it, and it doesn't combine with 了 or 过.

无 + noun

In notices and set phrases 无 stands alone before a short noun: 无人 "no one", 无效 "invalid", 无声 "silent", 无数 "countless". An everyday sentence still uses 没有.

• × 我今天无时间 → 我今天没有时间

"-less" and "non-"

As a prefix, 无 makes a describing word from a noun: 无糖 "sugar-free", 无线 "wireless", 无人机 "drone", literally "no-person machine".

无法 and 毫无

无法 + verb means "unable to", the written 没办法. 毫无 + noun means "not the slightest": 毫无意义, 毫无兴趣.

Not before a verb

无 denies having, not doing. An action that didn't happen takes 没 or 未.

• × 他无来 → 他没来
• × 我无去过北京 → 我没去过北京

无论, 无不 and 无非 are separate words with their own entries.