Regeneration

[Sarah]

The entering into a new spiritual life; the act of becoming, orof being made, Christian; that change by which holy affectations andpurposes are substituted for the opposite motives in the heart.He saved us by the washing of regeneration, and renewing of the HolyChost. Tit. iii. 5.

[Sarah]

[Time Lord]s appear human, but are different. [Time Lord]s can live for an extremely long time thanks to their ability to regenerate.
[Time Lord]s regenerate after suffering from mortal injury, illness, or old age.
Regeneration repairs and rejuvenates all damage. But a side effect is that it changes the [Time Lord]s physical appearance, and they gain a some what different personality.
Regeneration can be traumatic, and can leave the [Time Lord] disoriented, and weakened.

[Gregory]

the act of improving a place or system, especially by making it more active or successful:

[Tanya Shivari]

The action or process of regenerating or being regenerated, in particular the formation of new animal or plant tissue.