(mathematics, linear algebra, of a matrix) Not having full rank; having a rank (dimension) less than the number of columns and the number of rows.

(Cockney rhyming slang) A wank.

(Australia) Something fitting or occurring at a specified point in a series.

(law) The obligation of a barrister (in certain jurisdictions) to accept any work in a field in which they profess themselves competent to practise, at a court at which they normally appear, and at their usual rates.

(linear algebra) A theorem about linear transformations (or the matrices that represent them) stating that the rank plus the nullity equals the dimension of the entire vector space (which is the linear transformation’s domain).

(chess) A checkmate delivered by a major piece along the back rank against a king whose advancement is prevented by pieces of its own color (most commonly pawns).

plural of cab off the rank

(military) To march or charge out of the designated order in a military unit. / (idiomatic) To publicly disagree with one's own group or organization.

(military) To close the spacing between lines (ranks) of troops, as they are deployed across a battlefield, thereby decreasing the depth of the formation as it faces the enemy side.

Of the highest rank