unpromising; not to be relied on; of little hope
Describes a situation, prospect, or person that offers little expectation of success or reliability. Often used in the structure 期待薄だ or 期待薄の.
His success is unlikely.
This plan has an unpromising outlook.
Compound of 期待 (きたい, 'expectation') and 薄 (うす, 'thin, weak'). The exact historical derivation is uncertain, but the word follows a common pattern of noun + 薄 to express 'little of something'.