They do exist I can't find my book that had a picture or I'd post a link to a picture. Straight bladed scimitars aren't perfectly straight but it refers that it's taller and less curved that it's typical brother. they were used it area's that fighting was cramped and they couldn't get the clearance for the arc normally required for a scimitar.
-Grid

One of the problems with some modern classification systems is that they sometimes fail to take into consideration the culture that created a certain type of weapon. The cultures that used scimitars did not typically create swords that had any resemblance to the Christian longswords (which resembled a crucifix when inverted or held at leisure.) The straight-bladed scimitar (in the examples I have seen, not having added one to my collection yet) would have been the product of a culture that still used the moon amoung its symbols of devotion but wanted, as was mentioned, a blade more effective in close quarters where it wasn't possible to exploit the damage potential of the severely curved blade.

The modern taxonomy of the blade would more likely take into consideration only the design and function of the weapon, thus the potential confusion. The straight-bladed scimitar would be distinguished from a cutlass or blade of similar length/weight by the use of cross quillons (not basket or cup) and the slight curvature of the blade. The most distinguishing factor (IMO) would be the weighting of the blade. The weight of the scimitar was directed toward the front of the blade, not evenly as in the case of long and broad swords, but not as dramatically as weapons like the falchion.

Considering the definition of the scimitar typically includes reference to severe curvature it is easily possible to see where the confusion would come from.

Cheers - Cyllwdd's driver (who still cringes when seeing reference materials that define as morning-stars what are obviously long-hafted maces )

"camels and suck" such, not suck.