One knight under emotional strain and passionate (7)
I believe the answer is:
intense
'passionate' is the definition.
(I've seen this before)
'one knight under emotional strain' is the wordplay.
'one' becomes 'i' (Roman numeral).
'knight' becomes 'n' (chess abbreviation).
'under emotional strain' becomes 'tense' (I've seen this before).
'i'+'n'+'tense'='INTENSE'
'and' is the link.
(Other definitions for intense that I've seen before include "say, description of campers?" , "Highly emotional" , "Acute, exteme" , "burning" , "Concentrated, serious" .)