Emily Dickinson Lexicon

AP'ER-TURE, n.

1. The act of opening; more generally, an opening; a gap, cleft, or chasm; a passage perforated; a hole through any solid substance. – Holder. Newton.
2. An opening of meaning; explanation. [Not used.] – Taylor.
3. In geometry, the space between two right lines, forming an angle. – Encyc.