for all knows (adverb) perhaps: possibly
Sinonime: buttoning one's lip, buttoning up, clamming up, close-lipped, closemouthed, hidden, hush-hush, mum's the word, on the Q. T., private,
reticent, retired,
secluded,
secretive,
silent,
taciturn, tight chops, tight-lipped, uncommunicative, unforthcoming, zipping one's lips
Antonime: open, unreserved