といえども

1. 1Even X (someone or something you might expect to be an exception), the following still applies.Ex. 1
2. 2With どんなに／いかに／たとえ: no matter how X, the following still holds.Ex. 2
3. 3After a minimal quantity (e.g. 一日, 一円): not even that small amount, usually with a negative main clause.

This is a stiff, literary pattern used in formal writing, speeches, editorials, and statements of principle. The main clause typically states what should or should not be done (〜てはならない, 〜べきだ) or a result contrary to expectation. It is more formal than にしても or にしろ／にせよ, which express a similar concession in everyday language.

• とはいえN1「とはいえ」requires the preceding clause to be an established fact and sounds slightly softer than 「といえども」. It can also stand alone at the head of a sentence as a conjunction meaning “that said,” a use 「といえども」does not have.
• であれ / であろうとN1When attached to a noun to mean “even X,” 「であれ」is interchangeable with 「といえども」, and both belong to written language. However, it cannot attach to verbs or い-adjectives, often pairs with interrogatives like 「誰」and 「何」to cover every possible case, and its following clause can also state a general fact.
• とてN1Attached to nouns, 「とて」is close in meaning to 「といえども」and the two are often interchangeable. Attached to verbs or adjectives (usually in the た form), it works like 「たところで」, with the following clause typically being a futile, negative result; its tone is rather archaic, and it is also frequently seen in novels.
• にしてもN2「にしても」also expresses concession but in a plainer tone, is common in both speech and writing, and can replace 「といえども」in everyday conversation. It also has the parallel use 「AにしてもBにしても」, and 「だ」cannot be added after nouns or な-adjectives.
• にしろ / にせよN2「にしろ／にせよ」also expresses concession but is less formal than 「といえども」, and 「にしろ」is common in speech as well. It can also list alternatives as in 「AにしろBにしろ」or form 「いずれにせよ」, which 「といえども」cannot do; only the concession meaning is partially interchangeable between them.
• といってもN3「といっても」means “although it’s called X, it’s actually not that ...” and is used to lower expectations; it is neutral in register and can also serve as a sentence-initial conjunction. 「といえども」, with its formal tone, emphasizes “even X is no exception,” so the two generally cannot be interchanged.

Unlike とはいえ ("that said", which admits a fact and then qualifies it) and といっても ("although I say X, it's only…", which corrects an inflated expectation), といえども means "even X", and its main clause often states a rule that still applies. であれ／であろうと and とて are similarly formal "even/whether X" expressions, while にしても and にしろ／にせよ express a comparable concession in a more neutral, everyday register.