Frequently at no altitude at all (3)
I believe the answer is:
oft
'frequently' is the definition.
(synonyms)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for oft that I've seen before include "Quite frequently, according to the poet" , "time and again in literature" , "Consistently" , "Many a time to the poet." , "(Poetically) frequently" .)