abstract nonsense

³Lang’s Algebra [Lan02, p. 759] supports the general consensus that this was not intended as an epithet:

In the forties and fifties (mostly in the works of Cartan, Eilenberg, MacLane, and Steenrod, see [CE56]), it was realized that there was a systematic way of developing certain relations of linear algebra, depending only on fairly general constructions which were mostly arrow-theoretic, and were affectionately called abstract nonsense by Steenrod.