Does the basic left n right elbow in muay thai..............

[SpeedKills]

........travel a circular path like a boxing hook, or a straight lined path like a boxing straight right?

[TJ-Jitsu]

In short... YES

To be a little more specific, this means that the technique can do either or. Just the same way that "punch" is an umbrella term for hook, cross, overhand, etc, so too is "elbow."

Every way that a punch can be thrown so to can an elbow.

[sensei8]

After all...the elbow's connected to the...

[Alan Armstrong]

Muay Thai elbow strikes can also be used in every direction humanly possible. That about covers it ...