An adjective is a word whose main role is to modify a noun or pronoun, giving more information about the noun or pronoun's referent.
In Mapuzugun, adjectives do not agree neither in number nor in gender with the substantive. They are always placed before the noun they modify.
Adjectives in Mapuzugun can have a plural marker (see note about plural partitive at the footnote in this entry), which is formed by adding the end particle "-ke" to the adjective.
Fvxa (big) ce (people): The big people (grownup/s)
Fvxake ce: In this case, the meaning is "big people" (and not "the" big people)
Kvme (good) zomo (woman):
kvmeke zomo (good women and not "the" good women)
Adjectives do not agree with the gender of the modified noun.
Kvme (good) remanis unchanged, even before certain nouns that intrinsically mark a gender (e.g. wenxu = "man" and zomo = "woman")
Kvme wenxu = good man
Kvme zomo = good woman
Kvme caw = good father
Kvme ñuke = good mother
1. Demonstrative adjectives
Are formed by the Demonstrative Pronoun + the particle "-ci"
Tvfaci: this, these
Tvyeci: that, those
Tvfaci kawej: this horse
Tvfaci zomo: this woman
Tvyeci wigkul: that hill
Tvyeci ufisa: that seep
Note: "tvfa" and "tvye" without the particle "-ci" mean "here there is a..." and "there, there is a..."
Remember the absense of the verb "to be" in this kind of sentences.
Tvfa kawej: "here is a horse", "there is a horse here"
Tvye ufisa: "there is a sheep", "there is a sheep over there"
2. Possessive adjectives:
These adjectives mark possession (to whom something belongs)
1st pers. (iñce) ñi (my)
2nd pers. (eymi) mi (your)
3rd pers. (fey) ñi (his, her, its)
1st pers. (iñciw) yu (our: of the two of us)
2nd pers. (eymu) mu (yours: of you two)
3rd pers. (feyegu) ñi (their: of the two of them)
1st pers. (iñciñ) yiñ (our: of all of us)
2nd pers. (eymvn) mvn (your)
3rd pers. (feyegvn) ñi (their)
Note that both the possessive for the 1st person singular "iñce" and the possessive for the 3rd person in all groups are the same. If the speaker considers that this may be confusing for the hearer, the personal pronoun is added.
Iñce ñi ruka = my house
Fey ñi ruka = his house
Feyegu ñi ruka = their house (of the two of them)
Feyegvn ñi ruka = their house (of them all)
The particle "ta-" can be used, having only an expletiv function
Iñce ñi waka rume moxi (my caw is very fat)
Ñi waka rume moxi
Tañi waka rume moxi
Note: "rume" means "very". "Moxin" means: fat.
Iñciw yu kvzaw zoy kvmey
Our job is better or literally, "(we) our work more good"
Yu kvzaw zoy kvmey
Tayu kvzaw zoy kvmey
Note: "zoy" means "more". "Kvmen" (it a verb devived from "kvme" = "good") and means: "to be good".
The possessivo agrees with the subject in the sentence and is palced before the possessed noun.
Tvfa ñi meli kawej = these (are) my four horses (remember the verb "to be" is not in this kind of sentences)
This could also be: Tvfa iñce ñi meli kawej
Note: the adjective is placed between the possessivo marker and the noun.
Tvye (iñciñ) yiñ wenxu xewa = that (is) our dog.
 Cañumil, Tulio et al, op. cit.
Nota: the partitive plural is a grammatical number that is used to modify a noun which represents a part of some whole amount, as opposed to the comprehensive plural, used when the noun represents the total amount of something. The partitive indicates an indefinite quantity of a noun.
This case is not found in English.
In Mapuzugun the plural partitive marks a noun without specific identity.
Kiñeke ce koxv iyael kvmentukey = Some people like salty food.
Compare this with: Pu mapuce kvmentukey napor = The mapuche people like herbs
Re picike poñv xipay = We harvested only small potatoes
Fvtake kagkan mvley gijatun mew = There are big grills in a Guillatun 
Kuseke ufisa yafv ilo niey = Old sheeps have tough meat
 Catrileo, María, Diccionario Lingüístico-Etnográfico de la Lengua Mapuche, Ed. Andrá Bello, 1998
 The "expletive" function of a word (or particle, in this case) means that the word or particle performs a syntactic role but contribute nothing to meaning. It is used to complete or harmonize the phrase.
 Catrileo, Maria, Mapudunguyu - Curso de lengua mapuche, Univ. de Chile, Facultad de Filisofía y humanidades, 1988
Note: Maria Catrileo's book is written using the Unified Alphabet and the transcriptions in this entry were adapted by me. Should you find a mistake, please do write me an email or leave your comment for this entry.