sieve; sifter; strainer; colander; riddle (any device with holes used to separate solids from liquids or fine matter from coarse matter)

(idiomatic) a mind like a sieve

(cardinal number) seven (numerical value represented by the Arabic numeral 7; or describing a set with seven elements)

(transitive) to sift; to sieve

cloud nine

Transylvania

heptagonal, having seven corners

nominative/accusative/genitive plural of Sieb

(Catholicism) seven deadly sins

(Christianity, biblical) the book with seven seals mentioned in Revelation of John, verses 5:1 ff. / (figurative) closed book (something considered very hard to understand)