This paper examines the development and use of the temporal subordinator onmang þaet. The development of the subordinator is seen as a special case of grammaticalisation, i.e. incipient grammaticalisation. Onmang þaet arises through the incorporation of the prepositional phrase onmang + demonstrative into the subordinator structure and in this respect onmang þaet resembles the grammaticalisation of other OE subordinators. The grammaticalisation of onmang þaet is however arrested in early ME, as the paper shows using a generative approach. I interpret this turn in the grammaticalisation of the subordinator as indicative of incipient grammaticalisation and I further use this observation as an avenue to identifying other features concomitant with incipient grammaticalisation. What I suggest is that incipient grammaticalisation should be associated with low frequency, minimal erosion, lack of fusion, and, finally, specialisation. I tentatively argue that options reduced via specialisation, as is the case with onmang þaet, may be the ones that qualify as cases of incipient grammaticalisation. Importantly, what follows is that incipient grammaticalisation as discussed in this study is not to be taken as referring to the early stages of grammaticalisation as such but to the grammaticalisation of infrequent structures available for a longer period of time.