... and then there's analyses, which is the irregular plural form of the noun analysis. 

And there's also an analyst, which is a person who analyses (verb) things or who makes analyses. (plural noun).

How can you tell the difference?

The answer's in the stress pattern. The verb analyse/analyses has the stress on the first syllable (an) - as does the analyst, the person - while the noun analysis /analyses has the stress on the second syllable (nal).