dyad
Concise Oxford English Dictionary © 2008 Oxford University Press:
dyad /ˈdʌɪad/
▶noun technical something that consists of two elements or parts.
■ Mathematics an operator which is a combination of two vectors.
– derivatives
dyadic adjective.
dyadic adjective.
– origin C17: from late L. dyas, dyad-, from Gk duas, from duo ‘two’.
'dyad' also found in these Oxford entries:

