Tied up at work acquiring proficiency (8)
I believe the answer is:
aptitude
'proficiency' is the definition.
(thesaurus)
'tied up at work' is the wordplay.
'work' indicates anagramming the letters.
'tied'+'up'+'at'='tiedupat'
'tiedupat' with letters rearranged gives 'APTITUDE'.
'acquiring' is the link.
(Other definitions for aptitude that I've seen before include "Flair" , "fitness" , "Update it, having natural skill" , "faculty" , "Natural gift" .)