Some losing heart on romantic assignation, lacking fire (6)

I believe the answer is:

sedate

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'lacking fire' is the definition.
Although both the answer and definition are verbs in their base form, I can't see how one could define the other.

'some losing heart on romantic assignation' is the wordplay.
'losing heart' means to remove the middle letters.
'on' says to put letters next to each other.
'romantic assignation' becomes 'date' (I've seen this before).
'some' with its centre taken out is 'se'.
'se'+'date'='SEDATE'

Can you help me to learn more?

(Other definitions for sedate that I've seen before include "Calm - staid" , "Calm, not lively" , "Calm, unhurried" , "Dignified - staid" , "Calm, sober" .)

I've seen this clue in The Guardian.

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