The phrase "a main axis" is correct and usable in written English.
It can be used in contexts such as geometry, design, or discussions about structure and organization.
Example: "In the architectural design, the main axis serves as the central line around which the entire layout is organized."
Alternatives: "a primary axis" or "a central axis".
Lower metazoan forms developed the first symmetrical arrangement of body parts about a main axis, thus establishing the bilateral symmetry that characterizes most animals; major exceptions are the echinoderms (e.g., starfish and sea cucumbers).
The pollen-producing strobilus is a loose, pendulous, catkinlike structure consisting of a main axis to which are attached numerous appendages, each of which usually bears two microsporangia at its tip.
The city was almost completely destroyed by fire in 1720 and was rebuilt from a plan that gave it wide, regular streets and a main axis running east and west along the canalized Vilaine.
At the Angkor monument site, temples are positioned along a main axis that runs east to west.
Redundancy analysis extracted a main axis explaining 67% of the variation of the microbiological soil properties, which was interpreted as an environmental gradient of soil fertility.
The inflorescence usually consists of a main axis consisting of a peduncle and a rachis.
Tydemania forms more complex and larger thalli composed of whorls of siphons arising from a branched main axis.
Hyphae cottony white, mycelium aerial, conidiophore often visible in pustules, entirely fertile and plumose, symmetrical, comprising a recognizable main axis.
The columnar growth habit is characterized by a stunted main axis and the development of short fruit spurs instead of long lateral branches.
Amaranthus is a monoecious plant and the inflorescence is a thyrse with a racemose (catkin) main axis and cymose clusters (cymules) of one male flower and two or more female flowers.
Columnar apple trees show a characteristic pillar-like growth habit with a thick, stunted main axis and short lateral fruit spurs [ 1, 2].
