prefix of Germanic origin affixed to nouns and verbs and meaning "bad, wrong," from Old English mis-, from Proto-Germanic *missa- "divergent, astray" (source also of Old Frisian and Old Saxon mis-, Middle Dutch misse-, Old High German missa-, German miß-, Old Norse mis-, Gothic missa-), perhaps literally "in a changed manner," and with a root sense of "difference, change" (compare Gothic misso "mutually"), and thus possibly from PIE *mit-to-, from root *mei- (1) "to change."

Productive as word-forming element in Old English (as in mislæran "to give bad advice, teach amiss"). In 14c.-16c. in a few verbs its sense began to be felt as "unfavorably," and it came to be used as an intensive prefix with words already expressing negative feeling (as in misdoubt). Practically a separate word in Old and early Middle English (and often written as such). Old English also had an adjective (mislic "diverse, unlike, various") and an adverb (mislice "in various directions, wrongly, astray") derived from it, corresponding to German misslich (adj.). It has become confused with mis- (2).

Old English understandan "to comprehend, grasp the idea of, receive from a word or words or from a sign the idea it is intended to convey; to view in a certain way," probably literally "stand in the midst of," from under + standan "to stand" (see stand (v.)).

If this is the meaning, the under is not the usual word meaning "beneath," but from Old English under, from PIE *nter- "between, among" (source also of Sanskrit antar "among, between," Latin inter "between, among," Greek entera "intestines;" see inter-). Related: Understood; understanding.

That is the suggestion in Barnhart, but other sources regard the "among, between, before, in the presence of" sense of Old English prefix and preposition under as other meanings of the same word. "Among" seems to be the sense in many Old English compounds that resemble understand, such as underniman "to receive," undersecan "examine, investigate, scrutinize" (literally "underseek"), underðencan "consider, change one's mind," underginnan "to begin."

It also seems to be the sense still in expressions such as under such circumstances. Perhaps the ultimate sense is "be close to;" compare Greek epistamai "I know how, I know," literally "I stand upon."

Similar formations are found in Old Frisian (understonda), Middle Danish (understande), while other Germanic languages use compounds meaning "stand before" (German verstehen, represented in Old English by forstanden "understand," also "oppose, withstand"). For this concept, most Indo-European languages use figurative extensions of compounds that literally mean "put together," or "separate," or "take, grasp" (see comprehend).

The range of spellings of understand in Middle English (understont, understounde, unþurstonde, onderstonde, hunderstonde, oundyrston, wonderstande, urdenstonden, etc.) perhaps reflects early confusion over the elements of the compound. Old English oferstandan, Middle English overstonden, literally "over-stand" seem to have been used only in literal senses.

By mid-14c. as "to take as meant or implied (though not expressed); imply; infer; assume; take for granted." The intransitive sense of "have the use of the intellectual faculties; be an intelligent and conscious being" also is in late Old English. In Middle English also "reflect, muse, be thoughtful; imagine; be suspicious of; pay attention, take note; strive for; plan, intend; conceive (a child)." Also sometimes literal, "to occupy space at a lower level" (late 14c.) and, figuratively, "to submit." For "to stand under" in a physical sense, Old English had undergestandan.

"improperly understood, taken in a wrong sense," 1590s, past-participle adjective from misunderstand.

"want of understanding, mistake as to the meaning of something," mid-15c., misunderstonding, verbal noun from misunderstand.

When misunderstanding serves others as an advantage, one is helpless to make oneself understood .... [Lionel Trilling, "Art and Fortune," 1948]

Meaning "dissension, a disagreement, a quarrel" is recorded by 1640s.