semiangle noun2 •an angle of half a given size •The angle formed between the axis of a cone and a line drawn from the apex of the cone to the edge of its base.The author's theory is almost perfect for 5° semiangle, is good for M_∞ ≤ 2 with 10° semiangle, and is beginning to be a serious overestimate for 15° semiangle. — 1954 formssemiangles
