A host at last in position to calm down (7)
I believe the answer is:
placate
'calm down' is the definition.
(placating is a kind of calming down)
'a host at last in position' is the wordplay.
'at last' suggests the final letters.
'in' indicates putting letters inside.
'position' becomes 'place' ('place' can be a synonym of 'position'**).
The last letter of 'host' is 't'.
'a'+'t'='at'
'at' put into 'place' is 'PLACATE'.
'to' acts as a link.
(Other definitions for placate that I've seen before include "Make calm, conciliate" , "Mollify, calm down" , "Pale cat could pacify" , "Mollify, soothe anger" , "Mollify, appease" .)