Steer clear of a vacuum (5)
I believe the answer is:
avoid
'steer clear' is the definition.
(I've seen this before)
'a vacuum' is the wordplay.
'vacuum' becomes 'void'.
'a'+'void'='AVOID'
'of' acts as a link.
(Other definitions for avoid that I've seen before include "Steer clear of, dodge" , "Keep away from (someone/something)" , "Run away from" , "Shy away from" , "Fend off" .)