1) Addendum 2) Digression 3) Lark 4) Postscript 5) Rethink 6) Tergiversation 1) Change of mind 2) Exclusively Saxon word 3) Exclusively Anglo word 4) Flip-flop 5) Idea occurring later 6) Reconsideration 7) Reflection after an act 8) Rethink 9) Reversal 10) Second thought 11) Turnabout 12) Turnaround 13) Word with Anglo-Saxon origins 14) Word of purely Anglo origin 
• (n.) Reflection after an act; later or subsequent thought or expedient.
Aft'er·thought` noun Reflection after an act; later or subsequent thought or expedient. 
[n] - an addition that was not included in the original plan
noun an addition that was not included in the original plan; `the garage was an afterthought`
a later or second thought; reconsideration. · reflection after an act; an appropriate explanation, answer, expedient, or the like, conceived of too late for the occasion. · something added, as a part or feature, that was not included in the original plan or design: The vestry was added to the church as an afterthought.