noun

• (obsolete) A kind of coarse basket.
• (colloquial) A person, or their mind, that cannot remember things or is unable to keep secrets.
• (medicine, slang, derogatory) An intern who lets too many non-serious cases into the emergency room.
  "To be a sieve was to lack clinical judgment, courage, and group loyalty all at once."
• (category theory) A collection of morphisms in a category whose codomain is a certain fixed object of that category, which collection is closed under precomposition by any morphism in the category.

verb

• (sports) To concede; let in
  "This was their seventh defeat out of nine finals, including five in a row, and the second half was a chastening experience for the Serie A champions, culminating in them sieving more goals in one match than in the rest of the competition put together."