jganu -jga- gismu

x₁ is an angle [2-dimensional shape/form] from vertex x₂ subtended by lateral [segment] x₃.

Also (adjective:) x₁ is angular; x₂ corner; (segment x₃ can be defined by interval). See also kojna, linji, konju, mokca.

In notes:

cidni: x₁ is a/the knee/elbow/knuckle [hinged joint, body-part] of limb x₂ of body x₃.
kojna: x₁ is a corner/point/at-least-3-dimensional [solid] angle [shape/form] in/on x₂, of material x₃.
konju: x₁ is a cone [shape/form] of material x₂ with vertex x₃.
linji: x₁ is a line/among lines [1-dimensional shape/form] defined by set of points x₂.
mokca: x₁ is a point/instant/moment [0-dimensional shape/form] in/on/at time/place x₂.
radno: x₁ is x₂ radian(s) [metric unit] in angular measure (default is 1) by standard x₃.
cibjgacmaci: c₁ is trigonometry of triangle j₁.
te'odlito: x₁ is a theodolite (surveying instrument)