Sometime

(sŭm'-), adv. 1. At a past time indefinitely referred to; once; formerly. “Robert Scott, M. A., Prebendary of Exeter, sometime student of Christ-church, and late fellow of Baliol College.” Liddell & Scott's Gr. Lexicon.

That fair and warlike form In which the majesty of buried Denmark Did sometime march. Shak.

2Sense 2. At one time or other hereafter.

☞ Sometime is really a compound noun, and at is understood before it — at some time.