Etymology: Latin, adverb, more, from neuter of plur-, plus, adjective; akin to Greek pleion more, Latin plenus full — more at full
1. algebraically positive
2. having, receiving, or being in addition to what is anticipated
a. falling high in a specified range <a grade of C plus> b. greater than that specified c. possessing a specified quality to a high degree 4. electrically positive 5. relating to or being a particular one of the two mating types that are required for successful fertilization in sexual reproduction in some lower plantlike organisms (as a fungus) II. noun (plural pluses; also plusses) Date: 1654 1. plus sign 2. an added quantity 3. a positive factor or quality 4. surplus III. preposition Date: 1668 1. increased by ; with the addition of <four plus five> <principal plus interest> 2. besides — used chiefly in speech and casual writing <plus all this, as a sedative it has no equal — Groucho Marx> IV. conjunction Date: circa 1950 1. and <the Smyth Report, plus an idea and some knowledge of bureaucracy, were all I needed — Pat Frank> <eats alone, a hot beef sandwich plus a BLT plus apple pie — Garrison Keillor> 2. in addition to which <it was an achievement. Plus, I wrote the story and the musical score — Jackie Gleason> <it's also pretty on my open shelves, plus it smells good — Nikki Giovanni> Usage: The preposition plus has long been used with a meaning equivalent to and (as in “two plus two”); it is not, therefore, very surprising that in time people have begun to use it as a conjunction much like and. Sense 2 is considered to be an adverb by some commentators. It is used chiefly in speech and in informal writing.
New Collegiate Dictionary. 2001.