Worldly former sovereign having break during test (11)
I believe the answer is:
terrestrial
'worldly' is the definition.
(similar in meaning)
'sovereign having break during test' is the wordplay.
'sovereign' becomes 'er' (Abbreviation for Elizabeth Regina).
'having break' becomes 'rest' (I can't justify this - if you can you should give a lot more credence to this answer).
'during' indicates putting letters inside.
'test' becomes 'trial' (synonyms).
'er'+'rest'='errest'
'errest' placed within 'trial' is 'TERRESTRIAL'.
'former' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for terrestrial that I've seen before include "Not aquatic, arboreal, or aerial" , "Relating to the earth" , "Land-based" , "Relating to dry land" , "Living on the ground" .)