Nameless planet with rotation period of another, one of seven (8)
I believe the answer is:
saturday
'nameless planet with rotation' is the definition.
I can't tell whether this defines the answer.
'period of another one of seven' is the wordplay.
'period' becomes 'Sat' (Sat is an example).
'of another' becomes 'ur' (I can't justify this - if you can you should believe this answer much more).
'one of seven' becomes 'day' (I've seen this in another clue).
'sat'+'ur'+'day'='SATURDAY'
Can you help me to learn more?
(Other definitions for saturday that I've seen before include "Samedi or Sabato or Samstag" , "today?" , "Ian McEwan novel about day of the week" , "Day named for the sixth plant from the sun" , "24 hours" .)