(geometry) equilateral (referring to a polygon all of whose sides are of equal length)

(anatomy) knee

shadow / shade / darkness, murkiness / cloud of suspicion, of distrust / shadowy figure, apparition / ghost, specter / beauty, appropriation (when associated with speech, idiomatic expression, clothing, jewelry, decoration, etc.)

lighter (fire-making device)

painter (rope) / rope

artillery

aviation (art or science of flying)

I reduce, make fade, extinguish / I fail

spontaneous

apathetic (void of feeling)