arrowhead
target of a flying arrow; brunt (of an attack)
the very moment (when); the point (of doing)
出かける矢先に雨が降った。
It rained just as I was about to go out.
契約する矢先にトラブルが起きた。
Trouble arose just when we were about to sign the contract.
新しい仕事を始めようとした矢先に体調を崩した。
I fell ill just when I was about to start a new job.