Definition of "understand"

Thus, when he drew up instructions in lawyer language, he expressed the important words by an initial, a medial, or a final consonant, and made scratches for all the words between; his clerks, however, understood him very well.

1892, Walter Besant, “Prologue: Who is Edmund Gray?”, in The Ivory Gate […], New York, N.Y.: Harper & Brothers, […]

In reading this book, be very certain you never go past a word you do not fully understand.

1950, L. Ron Hubbard, Dianetics‎, New Era Publications, published 1999, page ix

‘I came back here, had a wank and finished that book.’‘The Naked Lunch?’‘Yeah.’‘What did you reckon?’‘Crap.’‘You're just saying that because you didn't understand it,’ said Adrian.‘I'm just saying that because I did understand it,’ said Tom. ‘Any road up, we'd better start making some toast.’

1991, Stephen Fry, The Liar, London: Heinemann, page 20

‘I understand that the district was considered a sort of sanctuary,’ the Chief was saying.

1963, Margery Allingham, “Foreword”, in The China Governess‎

Swearing doesn't just mean what we now understand by "dirty words". It is entwined, in social and linguistic history, with the other sort of swearing: vows and oaths.

2013 June 14, Sam Leith, “Where the Profound Meets the Profane”, in The Guardian Weekly, volume 189, number 1, page 37

LAUNE: Ay, and what I do too: look thee, I'll but lean, and my staff understands me.SPEED: It stands under thee, indeed.LAUNCE:Why, stand-under and under-stand is all one.

c. 1590–1591 (date written), William Shakespeare, “The Two Gentlemen of Verona”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act II, scene v]