Quote from http://wikipedia.org/wiki/engineer
"An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical problems. Engineers design materials, structures and systems while considering the limitations imposed by practicality, safety and cost. The word engineer is derived from the Latin roots ingeniare ("to contrive, devise") and ingenium ("cleverness")."
Software engineers definitely fall under this definition.
Would you trust dictionary.com? It agrees with Wikipedia.
Origin:
1350–1400; engine + -eer; replacing Middle English engin ( e ) our < Anglo-French engineor Old French engigneor < Medieval Latin ingeniātor, equivalent to ingeniā ( re ) to design, devise (verbal derivative of ingenium; see engine) + Latin -tor -tor
> Engineers design materials, structures and systems while considering the limitations imposed by practicality, safety and cost.
That's where I begin to say that computing comes up short as 'engineering':
The problem is that too often in computing the "design" work, just the design work alone, before construction, cannot really tell what the "practicality, safety and cost" will be. So, too often in computing we have to build the system and then test it to know what its "practicality, safety and cost" are. That was often the situation in the construction of medieval cathedrals: Some examples stood; some fell down; some on the borderline got weaker over time. Apparently eventually the strong cathedrals were built mostly drawing from experience, that is, closely copying what had already worked before. That technique is trial and error and copying and not really the 'design' of engineering.
If bridge engineering were the same as software construction, then just to know how strong the bridge was we'd just have to build the bridge and then test it. For rocket engineering, to know if it could reach orbit we would have to build and launch it. Indeed, instead, in rocket engineering we can determine the rocket trajectory that will put the maximum payload into the desired orbit.
Software engineers definitely fall under this definition.