Very old, prudish ring on Republican phone (10)
I believe the answer is:
primordial
'very old' is the definition.
Both the answer and definition are adjectives. Perhaps there's an association between them I don't understand?
'prudish ring on republican phone' is the wordplay.
'prudish' becomes 'prim' (synonyms).
'ring on' becomes 'o' (letter resembling a ring. I am not sure about the 'on' bit.).
'republican' becomes 'r' (abbreviation).
'phone' becomes 'dial' (dial phone is a kind of phone).
'prim'+'o'+'r'+'dial'='PRIMORDIAL'
Can you help me to learn more?
(Other definitions for primordial that I've seen before include "From the beginning of time" , "Having existed from the very start - limp or arid (anag)" , "from the first" , "Existing from the start of time" , "Original" .)