It slowly moves to the centre to get up outside (8)
I believe the answer is:
tortoise
'it slowly moves to' is the definition.
The definition suggests a singular noun which matches the answer.
'centre to get up outside' is the wordplay.
'centre' becomes 'to' (I can't explain this - if you can you should give a lot more credence to this answer).
'get up' becomes 'rise' (synonyms).
'outside' is an insertion indicator (some letters go outside others).
'to' going inside 'rise' is 'rtoise'.
'to'+'rtoise'='TORTOISE'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for tortoise that I've seen before include "Slow-moving land reptile" , "Shelled creature" , "Slow mover" , "One that kept leading Achilles" , "he's slow to eat lettuce etc" .)