1. 介于两个状态之间的;将要进入特定状态的
If you say that someone or something is on the cusp, you mean they are between two states, or are about to be in a particular state.

1. point formed by two intersecting arcs (as from the intrados of a Gothic arch)

2. small elevation on the grinding surface of a tooth

3. a thin triangular flap of a heart valve

Synonym: leaflet