A recent One Big Happy has Ruthie coping with an ambiguity in the English adjective occasional:
Ruthie, quite reasonably, understands occasional in its primary sense, semantically related to the adverb occasionally, but her grandmother is using it in one of its context-restricted idiomatic senses, in which it evokes the noun occasion (a “pseudo-adjective” use of the word).
(Hat tip to Benita Bendon Campbell.)
Here’s NOAD2 on occasional, giving the primary sense first and then three bulleted pseudo-adjective uses (starting with the use for furniture):
occurring, appearing, or done infrequently and irregularly [that is, only occasionally]: the occasional car went by but no taxis.
• (of furniture) made or adapted for use on a particular occasion or for irregular use: an occasional table.
• (of a literary composition, speech, religious service, etc.) produced on or intended for a special occasion: he wrote occasional verse for patrons.
• dated employed for a particular occasion or on an irregular basis: occasional freelancer seeks full-time position.
The primary sense is of interest on its own, because of its adverbial interpretation, shared by a set of other adjectives with a temporal component in their semantics: usual (the usual banal remarks), customary (the customary excuses), etc.