1.Today's Words

1)em-: word-forming element meaning "put in or into, bring to a certain state," sometimes intensive, from French assimilation of en- "in, into" to following labial stop (-b-, -p-, and often -m-), or from the same development in later Latin in- (to im-). "This rule was not fully established in spelling before the 17th c." [OED], but it is likely the pronunciation shift was in Old French and Middle English and spelling was slow to conform. Also a living prefix in English used to form verbs from adjectives and nouns (embitter, embody). In words such as emancipate, emerge, emit, emotion the e- is a reduced form of Latin ex-  before -m-.

eg. embody, embed, embankment 

2)be-: word-forming element with a wide range of meaning: "thoroughly, completely; to make, cause seem; to provide with; at, on, to, for," from Old English be- "on all sides" (also used to make transitive verbs and as a privative or intensive prefix), from weak form of Old English bi "by," probably cognate with second syllable of Greek amphi, Latin ambi and originally meaning "about" .

This sense naturally drifted into intensive (as in bespatter "spatter about," therefore "spatter very much"). Be- can also be privative (as in behead), causative, or have just about any sense required. The prefix was productive 16c.-17c. in forming useful words, many of which have not survived, such as bethwack "to thrash soundly" (1550s), betongue "to assail in speech, to scold" (1630s).

eg. beside, beneath, between

2.Extra Words

1)swap: c. 1200, "to strike, strike the hands together," of uncertain origin, possibly imitative of the sound of hitting or slapping. The sense of "to exchange, barter, trade" is first recorded 1590s, possibly from the notion of slapping hands together as a sign of agreement in bargaining (as in strike a bargain). Related: Swapped; swapping. The noun in this sense is attested from 1620s; earlier "a striking, an act of striking" (mid-13c.). Swap-meet attested from 1968, American English.

2)megalomania: "delusions of greatness," 1866, from French mégalomanie; see megalo- + mania "madness."

3)mendacious: 1610s, from Middle French mendacieux, from Latin mendacium "a lie, untruth, falsehood, fiction," from mendax (genitive mendacis) "lying, deceitful," from menda "fault, defect, carelessness in writing," from PIE root *mend- "physical defect, fault". The sense evolution of Latin mendax was influenced by mentiri "to speak falsely, lie, deceive." Related: Mendaciously; mendaciousness.

4)derogatory: c. 1500, from Late Latin derogatorius, from Latin derogatus, past participle of derogare "to take away, detract from, diminish," also "repeal partly, restrict, modify," from de- "away"  + rogare "ask, question; propose" (see rogation).

5)sultry: 1590s, "oppressively hot, close and moist" (of weather), ultimately from swelter + alteration of -y (2), either as a contraction of sweltry or from obsolete verb sulter "to swelter" (1580s), alteration of swelter. Figurative sense of "hot with lust" is attested from 1704; of women, "lascivious, sensual, arousing desire" it is recorded from 1940. Related: Sultriness.

3.Sigh No More - Much Ado About Nothing