noun
secret plan; secret scheme
A plan kept hidden from others, often with a strategic or conspiratorial nuance. Relatively formal and somewhat literary.
敵の秘計を見破った。
We uncovered the enemy's secret plan.
彼は会社乗っ取りの秘計を練っていた。
He was devising a secret scheme to take over the company.
Compound of 秘 (ひ, 'secret') and 計 (けい, 'plan'). The reading is on'yomi. The exact historical derivation is uncertain, but the word follows a standard Sino-Japanese compounding pattern.