Consider using part-of-speech matching

[waldoj]

It seems to me that we could get better results if we ensure that synonyms use the same part of speech as the term. For example, the top 10 most similar terms to "vehicle" are:

motor
motorcycle
self-propelled
powered
off-highway
semitrailer
vehicles
motorboat
off-road
late

But if we restrict this to nouns, we get:

motor
motorcycle
semitrailer
motorboat

That's a much better list of synonyms.

And for "improve":

enhance
achieve
restore
outcomes
low-income
replace
rehabilitate
growth
integrity
cost-effective

Whittling it down to verbs:

enhance
achieve
restore
replace
rehabilitate

Again, a much better list of synonyms.

The stumbling block here is that we don't know the part of speech for all defined terms. For example, "judge" could be a noun or a verb. But that's no reason not to use this process. The one caveat, of course, is that this necessitates having a machine-readable dictionary that we can use to determine the part of speech for each term.