kept secret, especially because it would not be approved of 私下的;偷偷摸摸的(尤指因为不会被批准) low wages were supplemented by surreptitious payments from tradesmen. 商人私下付的报酬补充了低工资。
late Middle English (in the sense 'obtained by suppression of the truth'): from Latin surreptitius (from the verb surripere, from sub- 'secretly' + rapere 'seize') + -ous