In the direction of the length; lengthwise along the end or from end to end.
From Old English 'ende' (end) plus 'lang' (long), forming an adverb describing directional orientation. This old English formation persists in some dialects.
Carpenters and builders love archaic words like 'endlong' because they're extremely precise—saying something goes 'endlong' removes all ambiguity about which direction you mean.
Complete word intelligence in one call. Free tier — 50 lookups/day.