(crossword puzzles) An unchecked square: one that is part of only one entry (i.e., across or down, but not both).

Third-person singular simple present indicative form of know / (nonstandard) All persons, singular and plural, present form of know.

plural of nonconformist

(inorganic chemistry, in combination) Four arsenic atoms in a compound / (inorganic chemistry) The molecule that constitutes yellow arsenic. (As₄)