So tube is moving slow? (6)
I believe the answer is:
obtuse
'slow?' is the definition.
(synonyms)
'so tube is moving' is the wordplay.
'is moving' indicates an anagram (letters are moved around).
'so'+'tube'='sotube'
'sotube' with letters rearranged gives 'OBTUSE'.
(Other definitions for obtuse that I've seen before include "angle, perhaps" , "Blunt - stupid - insensitive" , "A 3dn between 90 and 180 degrees" , "Slow, dull" , "Lacking in insight" .)