Relation between "trivial", "more than trivial", and "less than trivial"

The syntax of comparative expressions is complex. A number of ellipsis (omissions) can occur. See here for some examples, although yours is not listed there.

The reason why the expressions in your question can be ambiguous is because they are comparative constructions in which the quality on which the comparatives are being compared is omitted.

The sentence

This is less than trivial.

has the structure

<comparative 1> is less [quality omitted] than <comparative 2>

where comparative 2 is an adjective serving as a noun, nominative adjective and the quality is assumed to be inferred by the reader from the nature of the adjective used as comparative 2.

Let's look at some possible versions without omitting the quality.

This is less [trivial] than trivial.

or

This is less [complex] than trivial.

In these the quality is explicit. I chose the two examples to produce phrases with opposing meanings. The first one means that 'This' is more complex than something that would be considered trivial, while the second means that 'This' is more trivial than something that would be considered trivial.

We could have chosen an entirely different quality from these two. The meaning in that case would change even more. For example,

This is less a synonym than trivial.

would mean than 'This' and 'trivial' are being compared as being synonyms of something and 'This' is losing the competition. This time 'trivial' refers to the word 'trivial', though. In written English would have either a different font or quotation marks.

For other adjectives it might be easier to apply even more qualities.

• This is more than red.
• This is more red than red.
• This is more intense than red.
• This is more low-frequency than red.
• This is more romantic than red.

Having more options can make the phrase with the omitted quality even more ambiguous when looked without a context.

But then you have the cases in which due to the frequency of their usage the meaning is not ambiguous. For example,

I am more than happy to help.

means that I am very happy to help. The meaning is as if it were

I am more happy than happy to help.

The possibility of interpreting that the omitted quality could be, say, 'angry' as in

I am more angry than happy to help you.

is neglected because how much more frequently the first option is used.

Conclusion: The phrases with the general structure that you asked can be ambiguous, or not depending on the case, and on the context. Your searches about the specific examples of 'less than trivial' and 'more than trivial' indicate that people have used them both with the same intention. Therefore, the meaning would have to be inferred from the context. So, if it is you using it, then you better provide that context. If precision is essential, then one better use a less ambiguous phrase.

Trivial analysis that anyone can do:

• This type of phrases cannot be an anastrophe, since there is no reordering of the words that yields a normal order sentence.
• They are also not euphemisms. For example 'more than happy to help' definitely means happy.

What an interesting observation. I can totally see how this could be confusing.

I would interpret "less than happy" to mean "there is a scale of emotional satisfaction with 'unhappy' on one end, 'happy' in the middle, and 'joyful' on the other, and my current state is less than 'happy'", that is, closer to the unhappy end.

Similarly, I would interpret "less than trivial" to mean "there is a scale of difficulty with 'not at all difficult' on one end, then 'trivial', then 'hard', then 'infeasible', then 'impossible' on the far end, and this problem is less difficult than 'trivial'", that is, closer to the "not at all difficult" end.

However, I can totally see your point. We might instead interpret this as "there is a scale of ease with 'impossible' on one end, and 'not at all difficult' on the other end, and this problem is less easy than trivial."

Either interpretation makes sense, so I think it is a matter of custom. We are accustomed to thinking of happiness as being on a scale where "unhappy" is "low" and "joyful" is "high", but we could just as easily think of a scale of unhappiness", where "joyful" is the least amount of unhappiness. But that feels backwards; "happiness" is sort of the "primary" way to think of an emotional state, and "unhappiness" is derived from that.

But for "difficulty" verses "easiness", it's not so clear which one should be the primary scale we use to characterize a problem. I suspect that people in problem-solving fields tend to think of problems in terms of their difficulty and not their easiness; I would immediately think that "less than trivial" meant "very easy" and not "slightly harder than trivial".

Finally: this does not address your specific problem regarding comparisons, but it does discuss what engineers mean by "trivial"; it is both insightful and entertaining: https://fishbowl.pastiche.org/2007/07/17/understanding_engineers_feasibility