In this paper I consider the idiosyncratic development of the adverb long in such English idioms as I won’t be/take long. Various word classes have been proposed, including noun and preposition. I review examples from the OED and the Penn parsed corpora. Although adverb fits most of the contentious data best, the choice between adjective and adverb can be unclear.
We need not assume that every word in every grammatical sentence must belong to one and only one word class (Denison 2013). I suggest that in certain usages long exhibits adjective ~ adverb underspecification, and that such behaviour can be demonstrated in Old and Middle English. Other examples are offered of adjective ~ adverb underspecification. While long itself can be underspecified for class or can behave as a semi-grammatical, decategorialised word, at the phrasal level its distribution is less anomalous; furthermore, certain semantic and pragmatic features correlate with these usages. Accordingly, it is sensible to describe the history of such usages in Construction Grammar terms. Evidence from current Danish lends support to the scenario proposed, as well as providing useful morphological evidence of word class status.