klænˈdɛstɪn ˈhʌɡ.əˌmʌɡ.ə ˈhʌɡ.ɚˌmʌɡ.ɚ ɹɪˈzɪstəns ˈsiːkɹɪt ˈsʌbˌweɪ ˌsʌɹɪpˈtɪʃəs səˌɹɛpˈtɪʃəs tjuːb ˌʌndəˈɡɹaʊnd ˌʌndɚˈɡɹaʊnd ˌʌndəˈɡɹaʊnd ˌʌndɚˈɡɹaʊnd ˌʌndəˈɡɹaʊnd ˌʌndɚˈɡɹaʊnd beneath the surface of the earth water flowing underground in or into hiding or secret operation the organization was driven underground conducted with or marked by hidden aims or methods clandestine intelligence operations cloak-and-dagger activities behind enemy lines hole-and-corner intrigue secret missions a secret agent secret sales of arms surreptitious mobilization of troops an undercover investigation underground resistance under the level of the ground belowground storage areas underground caverns an electric railway operating below the surface of the ground (usually in a city) in Paris the subway system is called the ‘metro’ and in London it is called the ‘tube’ or the ‘underground’ a secret group organized to overthrow a government or occupation force