What it means
とて expresses a strong concession: even if or even though a condition is true, the result or judgment that follows still applies. It is mainly used in formal, literary, or emphatic writing and often follows expressions such as どれほど or いくら. With verbs, it commonly follows the past form; with nouns and な-adjectives, it commonly appears as だとて.
Usage note
とて is markedly formal and is not normally replaced by a polite counterpart. In ordinary conversation, constructions such as ても or たとしても are usually more natural.
Example sentences
どれほど綿密な計画だとて、予期せぬ災害の発生まで完全に防げるとは限らない。
Even if it is an extremely meticulous plan, it cannot necessarily completely prevent the occurrence of unforeseen disasters.
いくら専門家だとて、初めて見る資料の真偽を一目で見抜けるわけではない。
Even an expert cannot necessarily discern the authenticity of material they are seeing for the first time at a glance.