Rhombohedral crystal system is also known as the trigonal system. The crystallographic axes used in this system are of equal length. None of the axes are perpendicular to any other axis.
a = b = c
α= β = γ ≠ 90°
Generalic, Eni. "Rhombohedral crystal system." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
Glossary
Periodic Table