noun which may take the genitive case particle 'no'
unauthorized; without permission; unapproved
Used as a no-adjective to describe actions or things done without official permission.
You must not start construction without permission.
無許可のコピーは法律違反です。
Unauthorized copying is a violation of the law.
lack of permission; absence of authorization
Used as a noun to refer to the state of not having permission. Often appears in formal or legal contexts.
無許可が問題となった。
The lack of permission became an issue.
The contractor was carrying out the construction without a permit.
Unauthorized parking is subject to a fine.
They entered the factory grounds without permission.
無断 is a more casual, everyday word for acting without asking (e.g. 無断欠席), while 無許可 stresses lacking formal, official authorization.
無許可 stresses acting without obtaining official permission/license, whereas 無届け stresses failing to file the required notification, which may or may not require approval.
許可 means official permission or approval, while 無許可 describes something done without that permission.
無免許 specifically means lacking a license (e.g. driving without a license), whereas 無許可 refers more broadly to lacking any required permission or approval.
Compound of 無 (mu, 'without') and 許可 (kyoka, 'permission').