Synonyms of covertly

2 Syllables
slyly, wildcat, hush-hush
3 Syllables
stealthily, privily, secretly, dingily, duskily, sneakily, hazily
4 Syllables
insidiously, furtively, privately, obscurely, undercover, nebulously, tenebrously
5 Syllables
surreptitiously, confidentially, clandestinely, indefinably, underhandedly