Could you give some sources where plan means something different in the context of software development methodologies (the topic in question) and that most people in software engineering use that different meaning?
More importantly, is there a definition of "plan" in the context of software development where my claim fails? The claim that if requirements or designs change enough, some parts of your plan have to be thrown out?
The meaning I used is also a primary definition and often enough the first definition you'll find in dictionaries. [1] [2] [3]
Your first link seems to contradict you. "A proposed or intended course of action" covers everything from the roughest outlines to the most detailed sequences of steps.
Regardless, I'm not particularly interested in the dictionary definition. This is English, and what matters in English is how people actually use the word. You are literally the first person I've ever heard of who believes that "plan" is restricted to high levels of detail.
More importantly, is there a definition of "plan" in the context of software development where my claim fails? The claim that if requirements or designs change enough, some parts of your plan have to be thrown out?
The meaning I used is also a primary definition and often enough the first definition you'll find in dictionaries. [1] [2] [3]
[1] https://www.wordnik.com/words/plan
[2] https://www.thefreedictionary.com/plan
[3] https://dictionary.cambridge.org/us/dictionary/english/plan