kantu -ka'u- gismu

x₁ is a quantum/ray/elementary particle/smallest measurable increment of property/activity x₂.

Quantum ray (= bonka'u). (cf. selci for masses and most objects; ratni, gradu, gusni, nejni, linji)

In notes:

gradu: x₁ [magnitude] is a unit/degree of/on scale/reference standard x₂ (si'o) measuring property x₃.
gusni: x₁ [energy] is light/illumination illuminating x₂ from light source x₃.
linji: x₁ is a line/among lines [1-dimensional shape/form] defined by set of points x₂.
nejni: x₁ is energy of type x₂ in form x₃.
ratni: x₁ is an atom of element/atomic number x₂ of isotope number/atomic weight x₃.
selci: x₁ is a cell/atom/unit/molecule of x₂; x₁ is an indivisible, most basic subunit of x₂.
guska'u: x₁ is a photon.
zgika'u: k₁ is a music note (tone).
zgika'usni: s₁ is a music note (symbol).
kuarka: x₁ is a quark with flavor x₂.