Q:

Indisposed used erroneously

My friend used the work indisposable incorrectly, when he was really reaching for the word 'indisposed'.
However, he actually meant 'I was otherwise busy'.... Not the true meaning of indisposed...
What are the alternative words to diverge from 'indisposed' and mean something more like 'I was busy' (and I don't want to go into details)
Is it 'I was otherwise occupied'?  But that sounds deliberately obtuse..(Like I don't want to tell you anything)
Or 'I was busy'? Which sounds aggressive in the sense that 'Don't ask me any more'...
INDISPOSED in the sense he intended, meant 'I was busy taking care of something irrelevant to this context / meeting'....  Not at all aggressive..Just wanting to assuage pertinent questions
(Knowing full well that indisposed means to 'feel a little sick', so slightly diminished in potential...And 'may just stay home tonight' - as I am 'indisposed')

A:

I would just say, "I'm afraid I was tied up."

4 a : to keep busy · was tied up in conference all day
b : to preempt the use of · tied up the phone for an hour

But unless it's said with a certain tone of voice, it's not going to imply "and I don't want to go into details." I'm not sure if anything can without also sounding impolite.

Here is something interesting. I found this article on the increasing use of indisposed in the busy sense. The concluding two sentences are:

Rather than being used as a vague excuse, implying temporary illness, for not doing something or talking to someone, it’s now being used to mean simply “busy or unavailable.” Given a few more decades, this may become an accepted use of the word, but for the moment, as the reaction of your boss illustrated, it’s probably better to stick to a simple “tied up.”

