Etymology
Advertisement
morpho- 

before vowels morph-, word-forming element of Greek origin meaning "form, shape," from Greek morphē "form, shape; beauty, outward appearance," a word of uncertain etymology.

Related entries & more 
Advertisement
pyelo- 

before vowels pyel-, medical word-forming element used from mid-19c. in forming medical terms, from Greek pyelos "oblong trough, bathing-tub," a word of uncertain etymology, taken in modern scientific use for "pelvis."

Related entries & more 
actino- 
before vowels actin-, word-forming element meaning "pertaining to rays," from Latinized form of Greek aktis (genitive aktinos) "ray of light, beam of light; spoke of a wheel;" of unknown etymology. It is perhaps cognate with Sanskrit aktuh "light, ray," Gothic uhtwo "dawn, daybreak," Lithuanian anksti "early."
Related entries & more 
pn- 

consonant sound in some English words derived from Greek. The p- typically is silent in English but pronounced in French, German, Spanish, etc.

It is to be desired that it were sounded in English, also, at least in scientific and learned words; since the reduction of pneo- to neo-, pneu- to new-, and pnyx to nix, is a loss to etymology and intelligibility, and a weakening of the resources of the language. [OED]
Related entries & more 
-emia 

word-forming element in pathology meaning "condition of the blood," Modern Latin combining form of Greek haima (genitive haimatos) "blood," a word of no established etymology (replacing the usual IE word, represented in Greek by ear; possibly from uncertain PIE root *sei- "to drip" (compare Old High German seim "virgin honey," Welsh hufen), but according to Beekes this proposal "cannot explain the Greek vocalism."

Related entries & more 
Advertisement
miso- 

word-forming element of Greek origin meaning "hater, hatred," before vowels, mis-, from Greek misos "hatred," misein "to hate," of uncertain etymology, perhaps from a Pre-Greek word. It was productive as a word-forming element in ancient Greek, for instance misoagathia "hatred of good or goodness;" misoponein "to hate work." In English it formed many compounds now obscure or recherche, but some perhaps still useful, such as  misocapnic (adj.) "hating (tobacco) smoke," misocyny "hatred of dogs," misoneism "hatred of novelty."

Related entries & more 
re- 

word-forming element meaning "back, back from, back to the original place;" also "again, anew, once more," also conveying the notion of "undoing" or "backward," etc. (see sense evolution below), c. 1200, from Old French re- and directly from Latin re- an inseparable prefix meaning "again; back; anew, against."

Watkins (2000) describes this as a "Latin combining form conceivably from Indo-European *wret-, metathetical variant of *wert- "to turn." De Vaan says the "only acceptable etymology" for it is a 2004 explanation which reconstructs a root in PIE *ure "back."

In earliest Latin the prefix became red- before vowels and h-, a form preserved in redact, redeem, redolent, redundant, redintegrate, and, in disguise, render (v.). In some English words from French and Italian re- appears as ra- and the  following consonant is often doubled (see rally (v.1)).

The many meanings in the notion of "back" give re- its broad sense-range: "a turning back; opposition; restoration to a former state; "transition to an opposite state." From the extended senses in "again," re- becomes "repetition of an action," and in this sense it is extremely common as a formative element in English, applicable to any verb. OED writes that it is "impossible to attempt a complete record of all the forms resulting from its use," and adds that "The number of these is practically infinite ...."   

Often merely intensive, and in many of the older borrowings from French and Latin the precise sense of re- is forgotten, lost in secondary senses, or weakened beyond recognition, so that it has no apparent semantic content (receive, recommend, recover, reduce, recreate, refer, religion, remain, request, require). There seem to have been more such words in Middle English than after, e.g. recomfort (v.) "to comfort, console; encourage;" recourse (n.) "a process, way, course." Recover in Middle English also could mean "obtain, win" (happiness, a kingdom, etc.) with no notion of getting something back, also "gain the upper hand, overcome; arrive at;" also consider the legal sense of recovery as "obtain (property) by judgment or legal proceedings." 

And, due to sound changes and accent shifts, re- sometimes entirely loses its identity as a prefix (rebel, relic, remnant, restive, rest (n.2) "remainder," rally (v.1) "bring together"). In a few words it is reduced to r-, as in ransom (a doublet of redemption), rampart, etc.

It was used from Middle English in forming words from Germanic as well as Latin elements (rebuild, refill, reset, rewrite), and was used so even in Old French (regret, regard, reward, etc.).

Prefixed to a word beginning with e, re- is separated by a hyphen, as re-establish, re-estate, re-edify, etc. ; or else the second e has a dieresis over it: as, reëstablish, reëmbark, etc. The hyphen is also sometimes used to bring out emphatically the sense of repetition or iteration : as, sung and re-sung. The dieresis is not used over other vowels than e when re is prefixed : thus, reinforce, reunite, reabolish. [Century Dictionary, 1895]
Related entries & more