Septicidal is a particularly mean example of this sort of a word because not only is the -icidal bit is really nothing to do with killing, but the sept- bit is nothing to do with either decay (as in septicaemia) or the number seven (as in September),* either.
Septicidal is also a word where consulting the dictionary definition is almost certain to involve another search to discover what on earth it's going on about. Here's the Collins definition:
adj Botany (of a dehiscence) characterised by splitting along the sides of the seed capsule.
...and then, to make things even worse, you discover that dehiscence isn't in the dictionary.
Anyway, this is septicidal dehiscence:
By H. Zell - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10996361.
That picture is of the plant Ledum palustre, or wild rosemary (though it's really a rhododendron).
Anyway, as it happens the septi- bit in septicidal comes from septum, which is a dividing partition in a living thing. The -cidal bit does come from the idea of killing, though nothing at all hurt, let alone killed.
Ah well. Accusing botanists of being over-dramatic is a novelty, at least.
Word Not To Use Today: septicidal. The -cidal bit comes from the Latin caedere to kill. Septum comes from saeptum, a wall, from saepīre, to enclose.
*Okay, September isn't a great example, is it? Errr...septet, perhaps (which is like a quartet, but nearly twice the size).