Headdress that is at right angles initially (5)
I believe the answer is:
tiara
'headdress' is the definition.
(I know that tiara is a type of crown)
'that is at right angles initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'that is at right angles' is 'TIARA'.
(Other definitions for tiara that I've seen before include "High diadem" , "Decorative headgear" , "Top decoration" , "expensive headwear" , "Jewelled, ornamental headgear" .)