horizon on water / a horizontal or level line (perpendicular to the force of gravity)

horizon on land

vitamin D2

Synonym of リボフラビン (ribofurabin, “riboflavin”); vitamin B2

2.5D / (by extension, fandom slang) belonging to a grey area between "2D" (anime, etc.) and "3D" (live-action, etc.), such as voice actors

(geometry, engineering) extended line (usually as an auxiliary line) / extension of a traffic route (e.g. highway or railway line) / (figuratively) extension or result developed from an existing thing

(technology) Synonym of アンテナ (antena, “antenna”); an aerial (device for receiving or transmitting)

borders (outer lines) of a box

copper wire

reticle; crosshair