Literary genre initially lacking in motion, mostly calm (7)
I believe the answer is:
pacific
'calm' is the definition.
(I've seen this before)
'literary genre initially lacking in motion mostly' is the wordplay.
'literary genre' becomes 'scifi' (I've seen this before).
'initially lacking' means to remove the first letter.
'in' indicates putting letters inside.
'motion mostly' becomes 'pac' (I can't explain this - if you can you should give a lot more credence to this answer).
'scifi' with its first letter taken away is 'cifi'.
'cifi' placed into 'pac' is 'PACIFIC'.
Can you help me to learn more?
(Other definitions for pacific that I've seen before include "Non-combative" , "Non-combatant" , "steam locomotive?" , "A great ocean" , "mild" .)