small pieces of something dry that burns easily, used for lighting fires火种;引火物
We used some dry grass as tinder to light the campfire.我们用一些干草作为引子来点燃篝火。
The grass is tinder-dry (= so dry that it will burn easily), so there's a risk of fire.草非常干,一点就着,所以有发生火灾的危险。