@Gargron You could use something like worldnet. https://wordnet.princeton.edu/
Those two tags you gave would be very close together in terms of lexical semantics (each word has a similar meaning). Like if you look up "domain term categories" for election you can see how poll is related. http://wordnetweb.princeton.edu/perl/webwn?o2=1&o0=1&o8=1&o1=1&o7=1&o5=1&o9=&o6=1&o3=1&o4=1&s=election&i=2&h=10000000#c
If you could order tags in a way that total lexical distance in wordnet = distance in lexical rank. And then show tags that are within a range of lexical rank.