In the main meaning, abduct and kidnap are rigorously synonymous. In addition to that, abduct also has a meaning in physiology (as in abductor muscle): move a body part away from its rest position.
I too have searched for a definitive answer to this question and not found one. My own way of differentiating grammar from usage errors for my English language learners is as follows:
- If the mistake contravenes a generalizable rule for all members of that word class, then it is a grammar mistake. Otherwise it is a usage mistake.
For example:
He live in Frankfurt contravenes the rule that verbs in the 3rd person singular present simple tense require an -s (with the exception of modals), and is hence a grammar mistake.
My grandfather is a very high man is a usage mistake. We can formulate a rule that high applies to mountains not people. But the rule applies to one member of the word class only and hence the mistake is one of usage.
On this basis, these errors are grammar errors:
- I play tennis yesterday.
- Do you have dog?
- I live in Frankfurt since 10 year. (3 errors)
And these are usage errors:
- I always enjoy to sleep late on Sundays.
- What is the reason of your lateness?
- She replied she didn't know the answer.
The issue is of more than purely theoretical importance because learners need to know whether they should consult a grammar book or a good dictionary/usage manual to find out if what they have written is correct.
It is interesting to note that two excellent resources for English language learners both have the word usage in their titles:
Garner's Modern American Usage and Swan's Practical English Usage.
Garner's book exclusively contains what I personally would define as usage issues, while Swan's includes numerous entries on what I would term grammar; including negation, passive, modals, determiners, etc. So it seems that even the experts can't agree on the meaning of the word.
Best Answer
A dilemma is a choice between several options that are equally unfavourable.
A quandary is the state of being uncertain as to what you should do.
But dilemma is also used of the state of having a dilemma to solve, while quandary is also used of the cause of the quandary, so there is certainly a large overlap between these two.
Dilemma is still used by some to refer only two options (the original meaning) or at least where there are known options (as opposed to just "I don't know what to do about this"). Some people though use it more loosely to be more fully synonymous with quandary.
It would be an example of hyperbole to describe it as either. If you aren't a stickler for the dilemma = 2 things rule, then either is equally good (if over the top), otherwise it's only a quandary.
While they can be used interchangeably (hence the dictionaries listing them as synonyms as you say), dilemma does more often refer to the choice and quandary the mental and moral state of having to make it, which gives dilemma a slightly greater nuance of the difficulty faced, quandary a slightly greater nuance of the emotional response to it.