Get used to terrible ruin, to a point (5)
I believe the answer is:
inure
'get used to' is the definition.
(I've seen this in another clue)
'terrible ruin to a point' is the wordplay.
'terrible' indicates an anagram.
'to a point' becomes 'e' (compass point).
'ruin' anagrammed gives 'inur'.
'inur'+'e'='INURE'
(Other definitions for inure that I've seen before include "Harden against, make tough" , "Harden, make accustomed to" , "Harden or accustom as to something unpleasant" , "To give experience" , "Cause to become hardened to" .)