retainer

PLAYBACK written by Raymond Chandlerを読み始めました。この著者の小説を読むのは初めてですが、私でも名前を知っているほどですから有名な作家に違いありません。どんな話か楽しみです。
ある女性の尾行を電話で依頼されるところから話は始まりますが、この手の小説を読むなら覚えておいた方が良いと思われる単語が早速でてきました。
The girl is not to know she is being followed. This is very important. I am acting for a very influential firm of washington attorneys. Miss Vermilyea will advance you some expence money and pay you a retainer of two hundred and fifty dollars. I expect a high degree of efficiency. And let's not waste time talking.
"retain" は知らない単語ではありませんが、上の "retainer" の意味は分からないので辞書を見ます。
・Oxford English Dictionary: A fee paid in advance to someone, especially an attorney, in order to secure or keep their services when required.: The annual fee of $2,500 is a bargain when compared to the monthly retainer plus commission required for full representation.
・Collins Dictionary: a fee paid in advance to secure first option on the services of a barrister, jockey, etc: I mean a few hundred million worth of rich, with probably forty lawyers on retainer.

・Vocabulary.com: Professionals like lawyers or consultants are paid a retainer, which is a fee. The retainer ensures that they will be available to work for you when you need them. You will often pay an hourly rate on top of the retainer once the lawyer or consultant has worked enough hours for you to use up the retainer fee you paid.
なるほど、弁護士などに、例え具体的な相談はなくとも、毎月払うような費用がありますが、これが "retainer" ですね。