Japanese initially a very abstruse language (4)
I believe the answer is:
java
'language' is the definition.
(major programming language)
'japanese initially a very abstruse' is the wordplay.
'initially' suggests taking the first letters.
'very abstruse' becomes 'va' (this could be a standard abbreviation of which I'm unaware).
The initial letter of 'japanese' is 'j'.
'j'+'a'+'va'='JAVA'
(Other definitions for java that I've seen before include "Catlike" , "Coffee - computer programming language" , "Jakarta on this island" , "Large island; coffee type" , "Indonesian island noted for its coffee" .)