Ultimately obsolete little contraction which we still use occasionally today (3)
I believe the answer is:
een
'we still use occasionally today' is the definition.
I know nothing about this answer so I can't judge whether this works.
'ultimately obsolete little contraction' is the wordplay.
'ultimately' indicates one should take the final letters.
The final letters of 'obsolete little contraction' are 'EEN'.
'which' acts as a link.
Can you help me to learn more?
(Other definitions for een that I've seen before include "Even, poetically" , "Even to the poet" , "Literary form of even" , "Poetic form of even" .)