Fifth complement
Analogous to the octave complement, the fifth complement of a given fifth-reduced interval is its interval distance from the perfect fifth (3/2). It seems to be very useful as a way of conceptualizing and constructing more traditional-sounding triads, and even as a way of describing the relationships between different thirds.
History
The thought that the major third and the minor third complement or contrast each other may date well back to classical era, when triads in the form of root-3rd-P5 dominated the construction of chords. The term was seemingly coined by Flora Canou in September 2020. [1]
Examples
The following interval pairs are fifth complementary to each other