I do understand how attributive and predicative adjectives work, yet I can't find an easier way for learners to differentiate between both types - especially if such differentiation doesn't exist in their mother tongues.
I'd like to suggest that maybe a reference grammar might be able to help you here. For instance, the 2002 reference grammar by Huddleston and Pullum et al., The Cambridge Grammar of the English Language (CGEL), discusses this very issue: "Chapter 6 Adjectives and adverbs", part "4 Restricted function for adjectives", on pages 553-562.
CGEL, in "4.1 Attributive-only adjectives",
- Adjectives that do not normally occur except as (heads of) attributive modifiers include:
which includes an example list of 30 adjectives (e.g. drunken, future, mere, putative, umpteenth). In this part, they also discuss "Meaning differences between attributive and non-attributive uses".
They also discuss "Potential differences between attributive-only and ordinary attributive adjectives"; where they discuss the four properties that ascriptive attributive adjectives characteristically have, but most attributive-only adjectives lack one or more of them. The properties are: entailment, subset, modifiability, pro-form.
Then they go on and discuss "Some types of attributive-only adjectives". In this part, they say:
- Attributive-only adjectives are too numerous and semantically heterogeneous to permit a simple and exhaustive classification. Instead we will here illustrate and comment on some of the most important semantic types.
Some of those types are: degree and quantifying attributives, temporal and locational attributives, associative attributives, process-oriented attributives, modal attributives, particularizing attributives, expressive attributives, hypallage: transferred attributives.
CGEL, in "4.2 Never-attributive adjectives", discusses "Adjectives which can occur predicatively or postpositively, but not attributively". These include "Adjectives formed with the 'a' prefix", and provide an example list of 24 adjectives (e.g. afloat, aglitter, alike, averse).
Also, includes "Adjectives with complements". And also includes "A small set of other adjectives".
And then includes "Postpositive-only adjectives", which are described as:
- A handful of adjectives are restricted to postpositive function:
and they provide an example list of 6 adjectives (e.g. flowers galore, the President elect).
Okayee, my fingers are tired. Hopefully I haven't made too many typos. It seems to me that CGEL has a lot of good info in those pages that might help you out (pages 553-562).
Best Answer
It's a noun, but can probably be used attributively in most cases: stopgap.
{ODO}