Elder; aging or old age.
From Greek presbys old man, via post-classical Latin presbyter, elder.
This word is not often listed in dictionaries as a combining form as it occurs outside the medical field only in the set of words of which a key member is presbyterian, referring to a form of church government by representative assemblies of elected elders or presbyters. Specifically, with an initial capital, Presbyterian refers to a Christian church that is broadly Calvinistic in outlook. In such terms, elder suggests a person who is venerable or wise in years, not necessarily old.
In medicine, however, presby‑ always refers to the effects of physical aging: presbyphonia (Latin ‑phōnia, voice or speech), changes in a person's voice due to aging of the vocal cords; presbyopia (see ‑opia), deterioration in a person's near vision occurring with advancing age; presbycusis (see ‑acusis), deterioration of hearing with aging; presbycardia (Greek kardia, heart), impairment of heart function with age with no evidence of other heart disease; and presbyosmia (see ‑osmia), diminution or loss of the sense of smell associated with aging. Presbyatrics is an infrequently used synonym for geriatrics.