Tension in the air (6)
I believe the answer is:
strain
I believe this clue is a double definition.
'tension' is the first definition.
(synonyms)
'the air' is the second definition.
('strain' can be a synonym of 'air')
'in' is the link.
(Other definitions for strain that I've seen before include "Drain off" , "Pass through a sieve" , "Difficulty that causes tension" , "Remove by passing through a filter" , "Distinct breed; use a seive" .)