Ordeal around first half of autumn making one most tense (7)

'most tense' is the definition.
('taut' can be similar in meaning to 'tense')

'ordeal around first half of autumn' is the wordplay.
'ordeal' becomes 'test' (a testing situation).
'around' is an insertion indicator.
'first half of' suggests halving the letters.
'autumn' halved is 'aut'.
'test' going around 'aut' is 'TAUTEST'.

'making one' is the link.