secretly.

In an obscure, mysterious, or vague way; (sometimes) spec. in a figurative or allegorical way. Now rare.

In a mysterious manner; so as to create a sense of mystery; inexplicably, enigmatically, obscurely. Also (rare): in the manner of a religious mystery.

In a mystical manner; so as to inspire a sense of spiritual mystery, religious awe, etc.; mysteriously, obscurely.

Mystical presence or nature; mystical significance. in (also through) his mystery: in or by its mystical presence or nature. in (a) mystery…

Secretly; in a concealed manner. Obsolete. rare.

In a cryptic manner; occultly, enigmatically.

In the solemn, authoritative, or sententious manner of an ancient oracle.

In an occult or hidden manner; secretly; imperceptibly, latently.

Mysteriously; frighteningly.

In a mystifying or mystified manner.

in a sphinx-like manner.

In a mystifying manner; so as to cause mystification; perplexingly, inexplicably.