cusp /kʌsp/ BrE AmE noun
[ Date: 1500-1600 ; Language: Latin ; Origin: cuspis 'point' ]
1 . [countable] technical the point formed where two curves join
2 . be on the cusp of something [singular] to be at the time when a situation or state is going to change:
The country was on the cusp of economic expansion.
3 . on the cusp someone who was born on the cusp was born near the time when one ↑ star sign ends and another begins