noun
the only way; the sole course
Used to express that there is no alternative; often appears in phrases like 一途をたどる (to follow the only path) or 一途しかない (there is no other way).
彼は成功への一途を歩み続けた。
He continued walking the only path to success.
この状況では、撤退の一途しかない。
In this situation, there is no choice but to retreat.