desktop n.

mid-14c., "table especially adapted for convenience in reading or writing," from Medieval Latin desca "table to write on" (mid-13c.), ultimately from Latin discus "quoit, platter, dish," from Greek diskos (see disk (n.)).

The Medieval Latin word is perhaps via Italian desco. Used figuratively of office or clerical work since 1797. Meaning "a department responsible for a particular subject or operation at a large organization" is by 1918, probably earlier, though it is not always possible tell whether a literal desk is meant or not. Sense of "reception desk at a hotel, etc." is by 1963. Desk job, one that is done at a desk as opposed to at a work-bench or in the field, is attested by 1900; desk-work "work done at a desk" is by 1826.

"highest point," Old English top "summit, crest, tuft," from Proto-Germanic *toppa- (source also of Old Norse toppr "tuft of hair," Old Frisian top "tuft," Old Dutch topp, Dutch top, Old High German zopf "end, tip, tuft of hair," German Zopf "tuft of hair"); no certain connections outside Germanic except a few Romanic words probably borrowed from Germanic.

Few Indo-European languages have a word so generic, which can be used of the upper part or surface of just about anything. More typical is German, which has Spitze for sharp peaks (mountains), oberfläche for the upper surface of flat things (such as a table). The meaning "highest position" is from 1620s; the meaning "best part" is from 1660s. The sense of "dominant sexual partner" is by 1961.

To go over the top is World War I slang for "start an attack," in reference to the top of the trenches; as "beyond reasonable limits, too far" it is recorded from 1968. Top of the world as "position of greatest eminence" is from 1670s. Top-of-the-line (adj.) is by 1950.

also lap-top, in reference to a type of portable computer, 1983 (adjective and noun), from lap (n.1) + top (n.1), on model of desktop.