Despite alleged monstrosities like Finnish lentokonesuihkuturbiinimoottoriapumekaanikkoaliupseerioppilas and German Schützengrabenvernichtungsautomobil, compounds are often shorthand renderings of even longer constructions in Esperanto, like harbroso (“hairbrush”) from broso por haroj.
Broadly speaking, there are four different types of compound word in Esperanto — copulative, appositional, endocentric, and exocentric. In all cases, words are joined together by putting them next to one another, and, euphony permitting, by dropping the termination of the first word(s):
|elfo-festo||[festo de elfoj]||elf-party|
|elf-amiko||[amiko de elfoj]||elf-friend|
Compound words generally consist of a head (a word that expresses the basic meaning of the whole compound) and one or more modifiers. (E.g., handbrake consists of the head brake, the basic meaning of the compound, and hand, describing the sort of brake it is.)
In Germanic languages, the head usually comes last in a compound, but this varies from language to language — and often within the same language (e.g., English lockpick and pickpocket, Spanish chupacabra and fazferir). Esperanto uses the model of Greek and Latin derived international compounds, where the main element, if any, comes last (e.g., astronaut “star-sailor”, anthropophage “man-eater”).
Beyond this, compound words in Esperanto may observe additional rules, depending on which category they fall into:
Copulative and Appositional
These include words that denote the sum of all the elements (ex. bittersweet, from bitter and sweet) and words where the elements provide different descriptions for the same thing (ex. hunter-gatherer, from hunter and gatherer).
Such compounds are made by simply by joining two similar words (two adjectives of taste in the case of bittersweet, two nouns of occupation in the case of hunter-gatherer) in the usual way:
|dolĉacida||[dolĉa kaj acida]||bittersweet|
|ĉasistoj-kolektistoj||[ĉasistoj kaj kolektistoj]||hunter-gatherers|
|nigrablanka||[nigra kaj blanka]||black-and-white|
There appears to be no consensus as to whether such combinations constitute true compound words or not, and therefore whether or not to inflect each element in them separately — that is, whether to say nigrablankaj instagramoj or nigraj-blankaj instagramoj. For the time being, both are correct.
These are compounds where the first element denotes a special type of the last element (ex. railroad is a special type of road), and they include several sub-categories:
Noun, Verb or Phrase + Noun, Adjective, or Verb
These compounds begin as a noun, adjective, or verb followed by a prepositional phrase, like boat (propelled) by steam. They then attach the object of the preposition (in this example, steam) as a prefix to the first word, creating steamboat:
|dentobroso||[broso por dentoj]||toothbrush|
|proteinriĉa||[riĉa je proteino]||protein-rich|
|pistolbati||[bati per pistolo]||to pistol-whip|
|grizharulo||[ulo kun grizaj haroj]||grayhaired man|
|unokululo||[ulo kun unu okulo]||one-eyed man|
|La familio Lannister nanĵetas malgrandan Tyrion ĉiuvespere.||[ĵeto de nano]||The Lannisters dwarf-toss little Tyrion every night.|
|Ĉu iu diris “Tondro-furio, benita klingo de la ventoserĉanto”?||[serĉanto de vento]||Did someone say “Thunderfury, Blessed Blade of the Windseeker”?|
If the first element of a compound is effectively an adverb (proteinriĉa, pistolbati) and the ending isn’t or can’t be elided, the first element is written as a separate word: (proteine riĉa, pistole bati). See below.
Adjective or Adverb + Noun or Verb
This is a somewhat restricted category in Esperanto; blackboard is pronounced differently from black board in English, but that doesn’t happen in Esperanto. For an adjective or adverb to be the first element in a compound, it has to have an elidable ending. Otherwise, it’s a separate word.
|nigra listo||[nigra listo]||blacklist|
|rapidmanĝaĵo||[manĝaĵo preparita rapide]||fast food|
Determinative Adjective or Preposition + Adverbialized Noun
When an adjective that indicates which and not what kind or a preposition is combined with a noun, the resulting compound can only exist as an adverb or adjective — ĉiu tago (every day) can become ĉiutage, for example, but as a noun remains ĉiu tago, not ĉiutago, a word that wouldn’t logically mean anything.
|miaparte||[mia parto]-e||for my part|
|tiuokaze||[tiu okazo]-e||in that case|
Preposition + Verb
When a preposition is combined with a verb that can take an object, the preposition is treated as an adverb with an elided -e and the object of the compound is the object of the original verb:
|depreni ĉapelon||[de-e preni ĉapelon]||to take off a hat|
When the preposition is one of place and the verb one of motion, motion toward that place is implied, and the place becomes the verb’s object:
|eniri ĉambron||[iri al en ĉambro]||to enter a room|
Exocentric compounds differ from other sorts in that they denote something unexpressed by any single element in the compound. For example, silverback denotes not a type of back, but a male ape characterized by a silver back, and before-tax denotes not a type of tax, but profits reckoned before taxes.
Esperanto forms exocentric compounds in much the same way English does, except that compounds beginning with numbers or adjectives usually end in -ulo when used as nouns (ex., grizhara “grey-haired”, but grizharulo “grey-haired man”), effectively making them endocentric, not exocentric.
One should be cautioned that in compounds where the ending of the first element can’t be elided or doesn’t exist, the compound’s elements can be mistaken for separate words when spoken (ex. tripartaj diinoj “tripartite goddesses” vs. tri partaj diinoj “three partial goddesses”, subtaso “saucer” vs. sub taso “under a cup”). And as with endocentric compounds, if the first element is an adjective or adverb, either its ending must be elided or the element written as a separate word.
|trianguloj||formoj kun [tri anguloj]||triangles|
|ĉiutaga||io rilata al [ĉiu tago]||everyday|
|duvizaĝa||io havanta [du vizaĝojn]||two-faced|
|superhomo||io [super homoj]||superman|
|antaŭĉambro||io [antaŭ ĉambro]||ante-chamber|
Exocentric compounds beginning with a number are sometimes rendered synecdochically, but this isn’t recommended: unuokulo, dumastoj.