Definition of "unfathom"

[…] if the anatomists and physicians find it beyond their penetration to unfathom the mysterious depths in the texture, generation, growth, and operations, of the human body; […]

1823, M. Aikin, David Hughson, Memoirs of Religious Impostors from the Seventh to the Nineteenth Century

De Vortimer started up, and drawing his sword “By heavens,” said he, “tell me which of you have done this, or I will tear the secret from your hearts! This is some base plot, which I will unfathom ere you leave the chamber.”

1845, Love and Crime; or the Mystery of the Convent, page 66

“Scientific ” breeding is a subject worthy of much discussion, and one that has long engaged my closest attention. Happy should be the man able to unfathom its many mysteries.

1891, Richard Woods, A Practical Guide to Successful Pigeon Culture, page 41

A body in the forward zone, buried or unburied, is Each night freshly degraded like traitor-corpse, where his heavies flog and violate; each day unfathoms yesterdays unkindness; dung-making Holy Ghost temples.

1979, Thomas Dilworth, The Liturgical Parenthesis of David Jones, page 12

The King smells danger and will ship Hamlet off to England; Polonius wants to try one last time to unfathom the prince.

1992, Vincent Crapanzano, Hermes' Dilemma and Hamlet's Desire

A voiceover at our end warned that we might find it 'a bit of a mystery to unfathom what's going on'. But really it was not all that hard to unfathom. Even when you couldn't follow the American commentators you could tell they were talking sense.

2017, Clive James, Clive James On Television