secret plan; secret strategy
A confidential plan or stratagem, often with a connotation of cleverness or cunning. Used in contexts like business, politics, or games.
彼はライバル会社に対抗する秘策を練っている。
He is devising a secret plan to compete against the rival company.
その棋士は秘策を隠して対局に臨んだ。
The shogi player faced the match hiding a secret strategy.
秘策 is a secret strategy kept hidden until used, while 妙案 is simply a clever idea without any implication of secrecy.
Compound of 秘 (secret) and 策 (plan, scheme). The reading ひさく is the standard on'yomi combination.