a·gain 
(ə-gĕn)
(ə-gĕn)adv.
Idiom: 1. Once more; anew: Try again.
2. To a previous place, position, or state: left home but went back again.
3. Furthermore; moreover: Again, we need to collect more data.
4. On the other hand: She might go, and again she might not.
5. In return; in response: paid him again.
again and again
Repeatedly; frequently.
[Middle English (influenced by Old Norse i gegn, again), from Old English ongeagn, against.]