Dyad (δυάς) is the ancient Greek word for “two.” The ancient Pythagoreans considered the numbers 1-10 to embody certain qualitative aspects (in addition to their quantitative function). Speculation on the qualities of the first ten numbers is sometimes called “arithmology” by modern scholars, in order to distinguish it from from the modern sense of “arithmetic.”
On the Dyad (περὶ δυάδος):
“Among the virtues, they [i.e. the Pythagoreans] liken it to courage (ἀνδρεία): for it has already advanced into action. Hence too they used to call it ‘daring’ (τόλμα) and ‘impulse’ (ὁρμή).
“They also gave it the title ‘opinion’ (δόξα), because truth and falsity reside in opinion. And they called it ‘movement’ (κίνησις), ‘generation’ (γένεσις), ‘change’ (μεταβολή), ‘division’ (διαίρεσις), ‘length’ (μῆκος), ‘multiplication’ (αὔξησις), ‘addition’ (σύνθεσις), ‘partnership’ (κοινωνία), ‘relativity’ (τὸ πρός τι), and ‘the ratio in proportionality’ (λόγος… ἐν ἀναλογίᾳ). For the relation of two numbers is of every conceivable form.”
— The Theology of Arithmetic 7.15-8.4
- ἄα (aa) – body of water
- ἃ ἃ or ἇ ἇ (ha ha) –ha ha, an expression of laughter