A few prepositions (adpositions) can be turned into an adjective by way of the superlative suffix. These are:

Actually, it is rather strange for the comparative suffix to be added to a preposition, since the comparative is usually restricted to adjectives or adverbs. In fact, it can be thought that it is rather the adverbial use of these adpositions that is suffixed here. The adpositions involved all denote a spatial position, more specifically in an opposition to one of the other derivations in this field. In addition, there is the formation middelstemiddlemost, which must have been derived from the particle middel-, which only occurs as the first element of compounds, and is related to middenmiddle.

The adjectives formed in this way are mainly restricted to attributive use:

An exception is the idiomatical use in sailing races, as in

In practice, these formations usually entail an opposition: 'before' versus 'after', 'above' versus 'under', 'inner' versus 'outer'. The form middelstemiddle can be seen as expressing an intermediate position between these extremes. It is striking that exclusive concepts are involved, for instance wheels of a bicycle (either front or back, in it foarste / efterste tsjilthe front wheel / the back wheel), lips (upper or under, in de boppeste / ûnderste toskenthe upper teeth / the under teeth) or tracks (inner or outer, in de binnenste / bûtenste baanthe inner track / the outer track). There are no positions in between on the scale. That may also be the reason that the comparative form is not appropriate here, i.e. *de boppe-r-e laachthe above-COMP-INFL layerthe layer more situated to the top.

There is a semantic property that restricts these formations further: they can only have a specific reference, and cannot refer to a kind. Compare the following sentences:

To refer to a specific kind of wheels, Frisian takes recourse to a compound, in this case eftertsjillenafter-wheel-PLback wheels. It should be noted, however, that this use of superlative forms of prepositions with a specific reference is diminishing nowadays, under the influence of Dutch.