The adjective litje ‘small’ used to have an irregular neuter form littik. Nowadays, the neuter from litjet is in use. (Compare the Low German form ’n grotet Huus, which is often used instead of ’n groot Huus.)

Some adjectives or determiners cannot be inflected, for several reasons. (Determiners are included in this section. Some of them will be discussed in the sections on pronouns as well.)

Adjectives like allene ‘alone’ are only used predicatively (die Mon waas allene‘the man was alone’, *die allene Mon‘the alone man’).

Possessive adjectives like mienen, dienen (etc.) are also used predicatively, e.g.: aal wät mienen is, is ook dienen ‘all that is mine is also yours’.

Modern material adjectives like plastik are indeclinable: dälich hät man plastik Wonnen ‘today they have plastic bins’.

Geographical adjectives ending in -er, -ker or -tjer, -ster are indeclinable: ju Seelter Sproake ‘the Saterland Frisian language’, do Uutändjer Sträiten ‘the streets of Utende’, ’t Romelster August-Märked ‘Ramsloh’s august fair’.

Several quantifying adjectives (or determiners) are indeclinable: in älke Huus ‘in every house’, allerhound Seken ‘all kinds of things’, do bee Brure ‘both brothers’, fuul Ljude ‘many people’, (gans) min Autos ‘(very) few cars’, (noch) moor Soarten ‘(even) more species’, träierlai Frjuunde ‘three kinds of friends’, (do) uur Wäänte ‘(the) other boys’. However, some speakers inflect älk(e) ‘every’ like a regular adjective. Likewise, uurs(e) is in use today as a regularly inflected alternative to uur. The adjective min ‘few’ is rarely used. Instead, people often say nit fuul ‘not much/many’ or (man) ’n bitjen ‘(just) a bit’.

The adjective fuul is inflected in a particular construction: aal do fule Moansken ‘all those numerous people’.

The quantifying determiner poor ‘a few’ is indeclinable as well, e.g.: poor Buren ‘a few farmers’. This is an abridged form of ’n poor‘a pair of’, compare (‘n) bitjen ‘a bit (of)’.

The (plural) quantifying adjectives enige ‘some’, morere ‘multiple’ and oankelde ‘a few’ are inflected like normal adjectives. The quantifying adjective monich is inflected like a normal adjective as well (e.g. monige Ljude ‘many people’), but monich can also be used as a predeterminer: monich ’n Huus ‘many a house’ or monich wäkke ‘many people’.

The interrogative and indefinite determiner wäkke ‘what/which; some’ is inflected wäkker (m.), wäkke (f.), wäkker (n.) and wäkke (pl.), according to Fort’s dictionary (2015). In the sources, we find different forms, however. For instance wäkken ‘some people’ or wäk and wäkket (which [n.]).

The interrogative determiner wät foar ‘what (kind of)’ is indeclinable: wie häbe blouked wät foar ’n Nutsen die Kunstdunger broacht hät ‘we have seen what advantage fertiliser has offered’. Likewise: wät foar ’n riezige Rookmasse ‘what a gigantic lot of smoke’, wät foar Malöör ‘what a misery’, wät foar Hiere ‘what kind of hairs’.

The quantifying adjective alle ‘all’ is used attributively with plural nouns, just like enige ‘some’ or morere ‘several’, e.g.: alle Dege ‘all days’. Indeclinable aal modifies the whole noun phrase, e.g.: aal do Noachte ‘all nights’, aal hiere Sustere ‘all of her sisters’. The latter option is obligatory in the singular: aal ju Molk ‘all (the) milk’, aal dät Jäild ‘all (the) money’. There are exceptions to this generalisation, but they strike one as either fixed expressions or German calques: aal Mugelk ‘everything possible’, uut alle Wareld ‘from all the world’, alle stoatlike Gewalt ‘all stately authority’, alles Jood ‘all weeds’ (cf. German alles Unkraut). Aal is also used as a floating quantifier: dät is aal neen Gould wät glimt ‘not all that shines is gold’ (lit.: ‘what shines is not all gold’).

The quantifying adjective gans can modify a proper noun (i.e. a geonym): in gans Seelterlound ‘in all Saterland’, gans Swottefoan ‘all Swottefoan (Black-more)’. Historically, gans is the (Low) German replacement of heel, which in its turn exclusively means ‘intact’ nowadays. (Note that geonyms like Swottefoan are usually neuter, e.g. dät oolde Jerusalem ‘ancient Jerusalem’.)

Prenominal adjectives situated between possessive determiners and neuter nouns are often inflected as if they were in an indefinite context, e.g. mien ljoof (or: ljowet) Wucht ‘my sweet daughter’.

Possessive determiners like uus ‘our’ and hiere ‘her, their’ will be discussed separately (see: pronouns).

Many fixed expressions contain case endings from older language stages or borrowed from High or Low German. For instance: in fuller Flamme ‘ablaze’ (lit. ‘in full-er flame’). In the case of ju gjuchter Hound ‘the right hand’ and ju linker Hound ‘the left hand’, the original case endings have become intransparent. Besides, people tend to say ju linke Hound (etc.) nowadays, with regular adjectival endings.

The attributive adjective touken (from reconstructed toukumende, ‘coming’) is indeclinable, e.g.: touken Täisdai ‘next Tuesday’. The indeclinable adjective sälger ‘late, deceased’ is placed after the noun phrase: din Bäbe sälger ‘your late father’ (cf. Middle Low German sêliger gedechtnisse ‘of blissful remembrance’).

The element boas- in ’n Boaskäärdel ‘an impressive man’ (literally: ‘a boss guy’) is not an adjective. It is considered to be an affixoid (i.e. a modifying part of a compound that has almost become a prefix). It is not (anymore) a word, hence the spelling without a space.