With the advantage changing hands, or shifting back and forth among the available alternatives.

(idiomatic) So evenly matched that the advantage shifts from one to the other, and the outcome is uncertain.

plural of nip-out

(mining) The situation where the roof and thill approach each other, diminishing the usual thickness of the coal seam or extinguishing it completely.

plural of nip point

(manufacturing) A point of convergence between two rolling parts, or a rolling part and a stationary part, where all or part of the human body could become trapped and injured.

Alternative spelling of catnip

Alternative form of catnip

(slang) The brief accidental exposure of a woman's breast, usually partially and on the side.

plural of nip slip