Cue validity is the conditional probability that an object falls in a particular category given a particular feature (cue).
Some attributes are considered as more essential for a category than others. Thus, the notion of cue validity implies that attributes are differently weighted; some might be essential, others can be overridden with varying degrees of facility. Essential attributes have the highest cue validity for a certain category (Navarro 1998).
Cue validity is a more specific version of feature validity -- whereas cues tend to be more directly perceivable whereas features includes inferred or "deep" features as well as cues.