rare

The word 'rare' entered English in the late 15th century from the Latin 'rarus', meaning 'thinly sown, having a loose texture, infrequent'. This Latin term is thought to derive from the Proto-Indo-European root 'ere-', meaning 'to separate, to loosen'. The semantic journey is one of moving from a physical description of sparseness or looseness to an abstract description of infrequency. Thus, the core logic connecting the ancient root to the modern meaning is the concept of being widely spaced or not densely packed, whether referring to physical matter or to the occurrence of events.

The word 'rare' is a simplex word of Latin origin. It does not contain separable, productive morphemes in modern English that are direct substrings of the current spelling.