understand

Etymology

From Middle English understanden, from Old English understandan (“to understand”), from Proto-West Germanic *understandan (“to stand between, understand”), from Proto-Germanic *understandaną (“to stand between, understand”), equivalent to Old English under- (“between, inter-”) + standan (“to stand”) (Modern English under- + stand). Cognate with Old Frisian understonda (“to understand, experience, learn”), Old High German understantan (“to understand”), Middle Danish understande (“to understand”). Compare also Saterland Frisian understunda, unnerstounde (“to dare, survey, measure”), Dutch onderstaan (“to undertake, presume”), German unterstehen (“to be subordinate”).

verb

1. (transitive) To grasp a concept fully in one's mind, especially (of words, statements, art, etc.) to be aware of the meaning of and (of people) to be aware of the intent of.
   I'm sorry. I don't understand.
   Please try to understand. It's not you, it's me.
   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, →OCLC, page ix
2. To believe, to think one grasps sufficiently despite potentially incomplete knowledge.
   I understand that you have a package for me?
   In the imperative mood, the word “you” is usually understood.
   ‘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. 2013-06-14, Sam Leith, “Where the Profound Meets the Profane”, in The Guardian Weekly, volume 189, number 1, page 37
3. (humorous, rare, obsolete outside circus, acrobatics) To stand underneath, to support.