Terribly quaint and ultimately obsolete (7)
I believe the answer is:
antique
'obsolete' is the definition.
(thesaurus)
'terribly quaint and ultimately' is the wordplay.
'terribly' indicates anagramming the letters.
'and' says to put letters next to each other.
'ultimately' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'quaint' with letters rearranged gives 'antiqu'.
'antiqu'+'e'='ANTIQUE'
Can you help me to learn more?
(Other definitions for antique that I've seen before include "Lovely old piece" , "From the distant past" , "Item from an earlier time" , "Old-fashioned, outdated" , "Very old and possibly valuable" .)