E'er is a written shortening of ever, the same kind of cut as o'er from over. Poets used it to save a beat in the line: if e'er you see me. It means at any time, or always, just as ever does. For e'er is for ever. You will not hear it in normal talk; it lives in songs, hymns, and older verse. People say it like “air.” It feels old-fashioned on purpose — a costume word, not a mistake, and not a different meaning. Though actually, once you see the apostrophe as “a letter took a nap,” a lot of old poetry becomes less mysterious.

ever（曾經、無論何時）的詩語縮寫