Synonyms of unobserved

2 Syllables
hidden, secret, unseen
3 Syllables
stealthily, privily, secretly, curtained, neglected, unheeded
4 Syllables
unremarked, insidiously, unrespected, furtively, disregarded, unperceived, unnoticed, inconspicuous, overlooked
5 Syllables
undiscovered, unrecognized, underhandedly, clandestinely, unremembered, unconsidered, unobtrusive