Soldier dropped at party by ten? That seems impossible! (7)
I believe the answer is:
paradox
'impossible' is the definition.
(thesaurus)
'soldier dropped at party by ten? that' is the wordplay.
I cannot quite understand how this works, but
'soldier' could be 'para' (short for paratrooper) and 'para' is found in the answer.
'party' could be 'do' (do can informally mean a party) and 'do' is located in the answer.
'by' could be 'x' (as in 'multiplied by') and 'x' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'seems' acts as a link.
Can you help me to learn more?
(Other definitions for paradox that I've seen before include "Absurd or self-contradictory statement" , "self-contradiction" , "A statement that seems to contradict itself" , "Anomaly" , "An apparent absurdity" .)