The form inwisti was first published in the phrase: “changes of ‘mind-mood’ or inwisti” (MR/216). At the time, this word was generally assumed to be a singular noun meaning “mind-mood”: see Christopher Tolkien’s interpretation on MR/471. Later, a similar form inwis was published with the gloss “change of mind, mood” with a plural form inwissi (PE17/191). Helge Fauskanger suggested that inwisti may be a variant of inwis (QQ/inwisti). If this were the case, it is likely the proper gloss for inwisti would be the full phrase “changes of mind-mood” and it is a plural noun.
If inwisti is accepted as the plural of inwis, it would have a stem of inwist-.
inwis noun "change of mind, mood". A following, bracketed form inwissi is either the plural, the ancestral form or a variant (PE17:191; cf. inwisti). Likely, inwis is to have the stem inwiss- before endings (alternatively inwist-, see inwisti below, and compare the verb vista- "to change").