I've used "spaceless shingles" before now to avoid the need for synonym lists.
I can think of many word-pairs like "skin care" that, when collapsed into one word, mean the same thing but I struggle to think of examples where two words joined together (likethis) change their meaning as a result. This means you can generally index your shingles without a space and overcome your problem.
Note however that spaceless shingles are not without issues.