Extemporary, a.
1. Extemporaneous. "In extemporary prayer." Fuller.
2. Made for the occasion; for the time being. [Obs.] "Extemporary habitations." Maundrell.
Shades of meaning
Fernald has no entry of its own for extemporary; he lists it under extemporaneous.
He lists it without comment; the entries above explain its neighbors.