uncomprehending adj.

prefix of negation, Old English un-, from Proto-Germanic *un- (source also of Old Saxon, Old Frisian, Old High German, German un-, Gothic un-, Dutch on-), from PIE *n- (source of Sanskrit a-, an- "not," Greek a-, an-, Old Irish an-, Latin in-), combining form of PIE root *ne- "not." Often euphemistic (such as untruth for "lie").

The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. It underwent a mass extinction in early Middle English, but emerged with renewed vigor 16c. to form compounds with native and imported words. It disputes with Latin-derived cognate in- (1) the right to form the negation of certain words (indigestable/undigestable, etc.), and though both might be deployed in cooperation to indicate shades of meaning (unfamous/infamous), typically they are not.

It also makes words from phrases (such as uncalled-for, c. 1600; undreamed-of, 1630s; uncome-at-able, 1690s; unputdownable, 1947, of a book; un-in-one-breath-utterable, Ben Jonson; etc., but the habit is not restricted to un-; such as put-up-able-with, 1812). As a prefix in telegramese to replace not and save the cost of a word, it is attested by 1936.

mid-14c., "to understand, take into the mind, grasp by understanding," late 14c., "to take in, include;" from Latin comprehendere "to take together, to unite; include; seize" (of catching fire or the arrest of criminals); also "to comprehend, perceive" (to seize or take in the mind), from com "with, together," here probably "completely" (see com-) + prehendere "to catch hold of, seize."

The (partial) range of senses in Latin prehendere was "to lay hold of, to grasp, snatch, seize, catch; occupy violently; take by surprise, catch in the act; to reach, arrive at;" of trees, "to take root;" of the mind, "to seize, apprehend, comprehend," though this last sense is marked "very rare" in Lewis & Short.

It is a compound of  prae- "before" (see pre-) + -hendere, found only in compounds, from PIE root *ghend- "to seize, take." De Vaan regards the compound as Proto-Italic. Related: Comprehended; comprehending.

Compare the sense development in German begriefen, literally "to seize," but, through the writings of the 14c. mystics, "to seize with the mind, to comprehend."