tetrad

UK: /ˈtɛtræd/ US: (te′trad)

WordReference Random House Unabridged Dictionary of American English © 2025

tet•rad  (te′trad), n. 

1. a group of four.
2. the number four.
3. [Cell Biol.] a group of four chromatids formed by synapsis at the beginning of meiosis.
4. Chemistry a tetravalent or quadrivalent element, atom, or group.

• Greek tetrad- (stem of tetrás) group of four
• 1645–55

Collins Concise English Dictionary © HarperCollins Publishers::

tetrad / ˈtɛtræd/ noun

1. a group or series of four

Etymology: 17th Century: from Greek tetras, from tettares four