consistency is the quality of always behaving in the same way or of having the same opinions or standards, and also how thick, smooth or firm a mixture or liquid substance is.
The Oxford Advanced Learner's Dictionary marks the first sense uncountable and approving: "the quality of always behaving in the same way or of having the same opinions, standard, etc.; the quality of being consistent," as in "She has played with great consistency all season." Its second sense, countable or uncountable, reads "the consistency of a mixture or a liquid substance is how thick, smooth, etc. it is," with the example "The cement should have the consistency of wet sand." Oxford dates the word to the "late 16th cent. (denoting permanence of form): from late Latin consistentia, from consistent- ‘standing firm’ from consistere ‘stand firm or still, exist’."
Cambridge Dictionary defines the substance sense, countable or uncountable, as "the physical nature of a substance, especially a thick liquid, for example by being thick or thin, smooth or lumpy, etc." and the uncountable sense as "the quality of always behaving or performing in a similar way, or of always happening in a similar way," as in "They've won a few games this season but they lack consistency."
Dictionary.com gives four senses: "a degree of density, firmness, viscosity, etc."; "steadfast adherence to the same principles, course, form, etc."; "agreement, harmony, or compatibility, especially correspondence or uniformity among the parts of a complex thing"; and "the condition of cohering or holding together and retaining form; solidity or firmness." It records the word as "First recorded in 1585–95."