The words “lineament,” “linear,” and “lineation” have become increasingly popular since the advent of spacecraft and high-altitude aircraft images. With the increased usage has come a concomitant relaxation in the definitions of these terms, until the literature now is overwhelmed with conflicting and equivocal meanings. The need for clarification of these terms is clear. We propose a return to more fundamental conceptual definitions, based on original usage. We define the word “lineament” in an essentially geomorphological sense, on the basis of the usage introduced by Hobbs: A lineament is a mappable, simple or composite linear feature of a surface, whose parts are aligned in a rectilinear or slightly curvilinear relationship and which differs distinctly from the patterns of adjacent features and presumably reflects a subsurface phenomenon. The word “linear” is restricted to its original adjectival sense to avoid the increasingly popular but grammatically and conceptually incorrect nominative use. The word “lineation” is restored to its fundamental petrographic meaning: lineation is the one-dimensional structural alignment of internal components of a rock, is imposed by external agents, and cannot be depicted as an individual feature on a map. In addition, we suggest usages of “line” and “alignment” to refer to nongeologic features and (or) questionable features that do not fit proposed criteria and where definitional restrictions or implications may be a problem.