main-sequence

The term "main-sequence" is a modern astronomical compound, first used in the early 20th century following the development of the Hertzsprung–Russell diagram. The word "main" carries its core sense of "principal" or "most significant," derived from a Germanic root related to power and strength. "Sequence" originates from the Latin verb for "to follow," implying a logical order. Combined, the term literally denotes the "principal ordered series" of stars, which forms the dominant, diagonal band on the H-R diagram where stars spend the majority of their lifetimes in stable hydrogen fusion. This nomenclature logically captures the concept of this band being the primary, continuous sequence among the scattered plots representing various stellar types and evolutionary stages.

Structure: main (primary) + sequence (ordered series) - main: From Middle English, from Old English mægen meaning "strength, power," and influenced by Old Norse megin. In this compound, it functions as an adjective meaning "chief, most important." - sequence: From Middle English, from Old French, from Latin sequentia meaning "a following," from sequi "to follow." In this compound, it functions as a noun meaning "a continuous or connected series."