Grapheme
An orthographic symbol. Depending on what type of symbols you have, they can e.g. stand for entire words, as in Chinese, or for a single sound (phoneme), as in English. Some languages only write the consonants, like Hebrew. Other systems are syllabic, and so on... The common notation for graphemes is <grapheme>.


Phoneme
A phoneme is termed as "the smallest entity that carries meaning". They are the single sounds of a language. In an ideal world, every English letter would stand for a certain phoneme. Unfortunately, the world is not perfect, so you get a degree of ambiguity. Since our alphabet was designed for the sounds of Latin and not for the sounds of English, allowances have to be made, like sometimes using more than one letter to represent a single sound, e.g. "sh" for [ʃ]. The common notation for phonemes is /phoneme/.


Phone
How a phoneme is actually produced. The physical sound wave you actually produce. Sounds can change depending on which sounds surround them, as we've seen in the English plural example: the phoneme /s/ turns into the phone [z] in "birds", and [s] in "blocks". In "houses", is actually becomes two phones, because a helping vowel is added: [ɪz]. The common notation for phones is [phone].


Allophone
Allophones are different variations of the same phoneme. Which allophone you end up using depends on the sounds around it, and also on its position in a syllable or a word. Our plural example comes again to mind. Another oft cited example is final devoicing in German: At the end of a word, /b/, /d/ and /g/ are pronounced as [p], [t], and [k]. In the middle of a word, they are pronounced as [ b], [d] and [g]. Example: <Berg> (mountain) is pronounced with final [k], but <Berge> (mountains) is pronounced with final [g]. This pronunciation rule (phonological rule) often makes for quite an accent when Germans speak English, because /had/ and /hat/ both come out like /hat/.

Word stem
The basic form of a word, when you strip away all endings etc. e.g. listen in listening

Suffix
A word ending added to the stem, e.g. -ing in listening

Prefix
Like a suffix, only at the beginning of a word, e.g. under- in understatement

Circumfix
Add something both to the beginning and the end of the word simultaneously. Very rare in English, but I did find an example: em- -en in embolden. A common example is the German past participle ge- -t in gemacht (done, made; the word stem is mach).

Infix
Add something to the middle of the stem. The most popular example for this being abso-fraggin'-lutely and variations thereof.

Affix
This is a cover term, meaning a suffix, prefix, circumfix or infix.

Morpheme
Usually termed as "the smallest entity that changes meaning". This can obviously be a stem, because when you select an entirely different word you also say something different. Affixes also fall into this category, e.g. plural tells you you're talking about more than one of a thing. Things can get a bit tricky though, because you can express plural not only by adding the suffix -s, but also by modifying the stem without adding anything (foot - feet), or even by doing nothing at all (sheep - sheep).

Umlaut
You replace a vowel in the word stem with a different vowel, as in sing - sang, or German Haus - Häuser. A Gaelic example would be bòrd - bùird or fear - fir.


Palatalization/Slenderization
English does not use this means, but Gaelic does. One speaks of "palatalization of the final consonant", or simply of "slenderization". Example: balach (boy) - balaich (boys), [x] - [ç]. In some cases, this also works the other way around, e.g. the Genitive of màthair (mother) is màthar, [ɾʲ] - [ɾ]. Slenderization is marked orthographically by adding an < i> before the consonant. Note that the Gaelic umlaut examples I gave also have slenderization.


Initial Consonant Mutation
Initial consonant mutation means that the first consonant of a word changes. This seems very strange to us at first and takes some getting used to, so let me elaborate a bit. The origins of this process lie in the way the words run together in Gaelic. So, phonological rules that apply in the middle of a word also apply between the end of one word and the beginning of the next. Therefore, how the initial sound of a word is pronounced (in formal terms, which allophone is selected for the phoneme), also depends on the final sound in the preceding word. But what happens when the sounds at the end of words change? The reason for the change of the initial sound is gone, but the change can remain. If this happens with a consonant, we get initial consonant mutation, often simply called "mutation". This can take various forms, depending on what phonological rules originally applied. In Scottish Gaelic, there is only one form, and it's commonly termed as lenition, as it's felt like a lightening of the sound. Often, you can also see the term "aspiration" being used for lenition. This is not to be confused with aspiration as we know it from Lesson 4, which is why I will always say "lenition". In Gaelic, lenition is marked by adding an <h> behind the consonant that is lenited. Unfortunately, the lenition of l, n and r is not marked orthographically in modern spelling.

Example: Feasgar math (good evening, feasgar is a masculine noun, so you get [mah]) vs. madainn mhath (good morning, madainn is a feminine word, so you get [vãh]).

To compare with a language that will be more familiar to most of you, let's have a look at French liaison: The plural "les" is pronounced without final -s in "les maisons", but when you say "les amis", you suddenly add a [z] for the -s. Actually, this [z] starts the first syllable in "amis", so it has shifted over. Now, since romance languages took Latin as their role model, the changing of sounds at the beginning of words has always been frowned upon by those who made the norms. If the norm hadn't resisted these processes, we actually might have initial consonant mutation in modern French! Now, what happened in Gaelic is that Old Irish, which functions as the role model for the Celtic languages, is 800 years younger than classical Latin, and these changes had already happened then. Thus, mutation has always been part of the norm in the surviving Celtic languages. You can read more about the origins of lenition in Lenition and why that is your mothers fault @ akerbeltz.


Suppletion
You replace a word by something completely different. e.g. go - went. A Gaelic example would be the genitive of bean (woman), which is mnaoi.


Affixation
Just like in English, one way of forming the plural is by adding a suffix. In Gaelic, one of these is -an, as in cànan (language) - cànanan (languages). Prefixation is rather used in word formation, as in mì- + fortanach = mì-fhortanach (unlucky).


Reduplication
In reduplication, you repeat a word or part of a word. Example: Tha e math math (It is good good = good indeed).