Dy = 2 Tri = 3
For example:
In sociology, dyad refers to pairs of individuals such as couples, co-authors, twins; triad refers to three individuals such as a threesome, 3 authors, triplets, etc.
In biology, a dyad is a pair of sister chromatids occurring in prophase I of meiosis; a triad consists of 3 chromatids in prophase I.
In music, a dyad is a set of two notes or pitches; a triad is 3 notes or a triplet of notes or pitches