adverb/min də ʁjɛ̃/
discreetly, nonchalantly, unsuspiciously, innocently, sneakily; without realising it; you wouldn't think so, but
“Je pensais que ça serait vite fini, mais mine de rien, ça fait déjà quatre heures qu'on travaille.”
Literally, “appearance of nothing”, or more loosely translated as “it looked like nothing”.