Consider the following two examples:
I’ve heard more vicious rumors.
I’ve heard less vicious rumors.
Which of these examples, if any, can be considered ambiguous in interpretation?
Consider the following two examples:
I’ve heard more vicious rumors.
I’ve heard less vicious rumors.
Which of these examples, if any, can be considered ambiguous in interpretation?
Both of them are ambiguous; in fact, your first sentence has three potential interpretations. Let's look at that first.
Imagine you've just heard a nasty rumour about a friend, who knows that people have been spreading rumours about him. You might go to him and say
I've heard more vicious rumours [about you].
What you mean is that you have heard vicious rumours about him in addition to the ones you've heard already.
Now imagine someone you know has stated in conversation how many vicious rumours they have heard to date, and you have heard a higher number. You might say
I've heard more vicious rumours [than you have].
What you mean is the the quantity of vicious rumours you've heard to date exceeds that of your friend.
Now imagine that you've just found out someone has been spreading a nasty rumour about you, but it isn't as bad as other ones that have been spread about you in the past. You might say
I've heard more vicious rumours [than that one].
In this case, rather than "more" being used for quantity, you're using "more vicious" as a modifier for "rumours", saying that you have heard rumours before which are more vicious than the one being discussed.
Some ambiguity exists with the second sentence as well; however, this is mainly because people usually mistakenly use "less" when referring to countable nouns (which rumours are) so if you meant you had heard a lower quantity of rumours than someone else, you'd actually say
I've heard fewer vicious rumours [than someone].
This eliminates the ambiguity as when you use fewer, it's clear you mean quantity, and in an ideal world where people knew the difference, saying
I've heard less vicious rumours [than that one].
Would be obviously interpreted as meaning the same as the third example from the first sentence.