OBSTACLE VS. OBSTRUCT

My mother, for whom English is a second language, frequently misappropriates the terms obstacle and obstruct to create the imaginary word obstrucle. This provoked an interesting thought: both words cover similar concepts and sound similar, so are they etymologically related? Turns out the two are more like cousins than brothers. Obstruct is from the Latin word obstruere, which meant "hinder" and is a portmanteau of the prefix ob- ("against") and struere, or "to build". Thus an obstacle hindered building. Struere is from the Latin word for "heap", strues, from the Proto-Italic term strowo, meaning "pile up", which in turn derives from the Proto-Indo-European root strew, which meant "to spread". Semantic connections are clear. Next is the word obstacle. This is through French and traces to the Latin noun obstaculum, which meant "a hindrance", a combination of ob- (the same root as before), -culum (a suffix), and sto, or "to stand". Sto, being the root I'm etymologizing, is from the Proto-Indo-European root sta, also "to stand". Thus it may be concluded that despite their close definitions describing hindrances, all obstacle and obstruct have in common are the first two  letters, which define the words, since as a morpheme they mean "against". Nothing else in common: wow!