Under the moonlight, they leaned in so close it became an almost-kiss, but ended up just smiling at each other.

almost-kiss 是由副词 almost（几乎）和名词 kiss（吻）组成的复合名词，中间用连字符连接。almost 表示"差一点、接近"，kiss 指"亲吻"。almost-kiss 描述的是"两人靠近到几乎要接吻但最终没有真正亲吻的状态"，可以理解为"差一点发生的吻"或"似吻非吻的暧昧时刻"。