Based on an earlier design (12)
I believe the answer is:
premeditated
'based' is the definition.
Both the answer and definition are adjectives. Maybe you can see a link between them that I don't see?
'on an earlier design' is the wordplay.
I cannot really understand how this works, but
'on' could be 'at' (I've seen this in other clues) and 'at' is found within the answer.
'an' could be 'i' (Roman numeral for one) and 'i' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for premeditated that I've seen before include "Planned beforehand" , "Considered" , "Planned in advance" , "Thought out beforehand" .)