Its meaning forked in English. Via the notion of "coarse in texture or quality" came the senses "not sensitive, dull stupid" (1520s), "vulgar, coarse in a moral sense" (1530s). Via notion of "general, not in detail" came the sense "entire, total, whole, without deductions" (early 15c.), as in gross national product (1947). Meaning "glaring, flagrant, monstrous" is from 1580s; modern meaning "disgusting" is first recorded 1958 in U.S. student slang, from earlier use as an intensifier of unpleasant things (gross stupidity, etc.).
early 15c. (mid-13c. as a surname), "wholesale dealer, one who buys and sells in gross," corrupted spelling of Anglo-French grosser, Old French grossier, from Medieval Latin grossarius "wholesaler," literally "dealer in quantity" (source also of Spanish grosero, Italian grossista), from Late Latin grossus "coarse (of food), great, gross" (see gross (adj.)). Sense of "a merchant selling individual items of food" is 16c.; in Middle English this was a spicer.
Figurative sense of "absorb the whole attention" is first attested 1709. A parallel engross, meaning "to write (something) in large letters," is from Anglo-French engrosser, from Old French en gros "in large (letters)." Related: Engrossed; engrossing.