What it means
たりとも marks an extremely small amount or a single member as an exception that is not allowed, usually meaning “not even” or “not any.” It commonly follows a number and counter, especially in forceful negative statements, and it can also follow a noun in highly formal or literary expressions. The construction emphasizes an absolute restriction, refusal, or lack of tolerance rather than merely stating that something is unlikely.
Usage note
たりとも is strongly formal, written, and rhetorical. It is often used with negative expressions such as ない, ぬ, or てはならない, and it must not be confused with the separate たり...たり pattern for listing actions.
How to use it
専門家たりとも油断してはなりません。
Even experts must not let their guard down.
私は一歩たりとも後退しません。
I will not retreat even one step.
専門家たりとも油断してはならない。
Even experts must not let their guard down.
私は一歩たりとも後退しない。
I will not retreat even one step.
Example sentences
この研究所では、機密資料を一部たりとも外部に持ち出してはならない。
At this research institute, not even a single part of the confidential materials may be taken outside.
納期を一日たりとも遅らせてはならない。
The delivery deadline must not be delayed by even one day.
災害時には、水を一滴たりとも無駄にしてはならない。
In times of disaster, not even a single drop of water must be wasted.