en cachette signifie anglais

secretly▼◼◼◼(in a secret manner)
adverb
[UK: ˈsiː.krɪt.li] [US: ˈsiː.krət.li]

on the sly▼◼◼◻(slyly, in an inconspicuous manner, so as not to be seen; secretly; stealthily)
adverb
[UK: ɒn ðə slaɪ] [US: ɑːn ðə sˈlaɪ]

unobtrusively▼(in a manner that is not noticeable or blatant)
adverb
[UK: ˌʌ.nəb.ˈtruː.sɪ.vli] [US: ˌʌ.nəb.ˈtruː.sɪ.vli]