Curvilinear

From Ferdinand de Saussure, Course in General Linguistics--

The linguistic sign, being auditory in nature, has a temporal aspect, and hence certain temporal characteristics: (a) it occupies a certain temporal space, and (b) this space is measured in just one dimension: it is a line

This principle is obvious, but it seems never to be stated, doubtless because it is considered too elementary. However, it is a fundamental principle and its consequences are incalculable.