Where does “floorboard” come from?

I can't write this etymology because the chain provided contains only English words repeating in a cycle (back, backboard, back, backboard...) with no connection to "floor" or "floorboard," and no original languages or meanings are supplied to trace the actual etymology. A valid chain would need to show the actual linguistic ancestry—for example, how "floorboard" relates to "floor" and "board," and what those words derive from in earlier languages. Could you provide the correct etymological chain?

floorboard (English): Any of the long boards laid over joists to make a...

Definitions

  1. Any of the long boards laid over joists to make a...

Ancestry of “floorboard”, step by step

floorboard traces back through two separate lines of ancestry.

via English board

StepLanguageWordMeaning
1EnglishboardA relatively long, wide and thin piece of any...
2Englishboardridersurfer
3EnglishriderOne who rides, often on a horse or a motorcycle;...
4Middle EnglishridereAlternative form of ryder
5Middle EnglishryderA rider or equestrian; one who rides a horse; A...
6Old Englishrīdererider, knight
7Old Englishrīdanto ride
8Proto-West Germanicrīdanto ride
9Proto-Germanicrīdanąto ride
10Proto-Indo-Europeanrēydʰ-
11Proto-Indo-Europeanh₂er-to fit, to fix, to put together

via English floor

StepLanguageWordMeaning
1EnglishfloorThe interior bottom or surface of a house or...
2Middle EnglishflorA floor; the bottom surface of a room or...
3Old Englishflōrfloor, pavement, ground; floor, pavement, ground,...
4Proto-Germanicflōrazground; floor
5Proto-Indo-Europeanpleh₂rosflat; floor
6Proto-Indo-Europeanpleh₂-flat

Words derived from “floorboard

Every word from Proto-Indo-European h₂er-