letting cat out of bag (verb) expose: reveal
Sinonime: ad-lib, extemporaneous, improv, improvised, improviso, off-hand, played by ear, shot from the hip, spontaneous, spur-of-the-moment, unpremeditated, unprepared, unrehearsed, unscripted, whipped up, winged*
Antonime: conceal,
cover,
hide