[/nq] Tinder is something that can catch on fire easily (like kindling). It may be used to start a fire because it will burn before larger pieces of wood will burn. I have never seen "tinderstick" as a single word, but it would probably mean a small stick that is used as tinder to start a fire.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.