Little-known degree held by Guardian's head of entertainment (7)
I believe the answer is:
obscure
'little-known' is the definition.
(I've seen this before)
'degree held by guardian's head of entertainment' is the wordplay.
'degree' becomes 'BSc' (Bachelor of Science degree).
'held by' means one lot of letters goes inside another.
'guardian's' becomes 'our' (belonging to the newspaper the puzzle is part of).
'head of' suggests taking the first letters.
The first letter of 'entertainment' is 'e'.
'bsc' going into 'our' is 'obscur'.
'obscur'+'e'='OBSCURE'
(Other definitions for obscure that I've seen before include "Hazy or cryptic" , "Dim, indistinct or not well known" , "Cloudy or veiled" , "Insignificant" , "Like Jude, not well known" .)