qualitative describes anything of, relating to, or involving quality or kind — concerned with what a thing is and what it is like, rather than with how much of it there is.
The word marks a category of evidence, not a lower grade of it. Qualitative research works through interviews, open-ended responses, observation, and field notes, and its output is a description dense enough that a reader can recognize the thing described. Because it does not fix its questions in advance, it can register what nobody thought to ask about — the reason it usually comes first, generating the categories a 📝quantitative instrument later counts. Every closed survey option was once someone's qualitative reading of an open answer. In chemistry the sense is narrower and older: qualitative analysis identifies which constituents a sample contains, leaving the amounts to a separate procedure.
The term reaches English in the early fifteenth century as qualitatif, "that produces a physical quality," from Medieval Latin qualitativus and Latin qualitas, "a quality, property, nature." Behind it stands qualis, "of what kind," from the Proto-Indo-European stem kwo- that yields the relative and interrogative pronouns. The current sense, concerned with quality without reference to quantity, settles in around 1600 under the influence of French qualitatif.
The same qualis root produces 📝Qualia, the philosophical term for the felt character of an experience — the redness of red, what a particular wine tastes like — which marks the far edge of what qualitative description reaches for and what no measurement captures. The method's cost is the mirror of its strength: findings drawn from few cases resist generalization, and interpretation is difficult to separate from the interpreter, which is why qualitative work is reported with its method exposed rather than as a bare result.