Once a class to rely strangely on (8)
I believe the answer is:
formerly
'once' is the definition.
(I know that once can be written as formerly)
'a class to rely strangely on' is the wordplay.
I cannot really understand how this works, but
'class' could be 'form' (synonyms) and 'form' is present in the answer.
an anagram of 'rely' is 'erly' which is within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for formerly that I've seen before include "At one time" , "Hitherto" , "Previously, before this time" , "In the past" .)