From even + down. Compare downright.
evendown (comparative more evendown, superlative most evendown)
- (Scotland) Being situated straight up and down; perpendicular to ground level; downright.
- (Scotland) (of rain) Heavy.
- (Scotland) Downright; direct; straightforward; candid.
- (Scotland) Out-and-out; plain; flat; flat-out.
- What you told me is an evendown lie!
- (Scotland) Mere; sheer.