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").
Quenya
inwis
noun. change of mind/mood
inwis
change of mind, mood
inwisti
mind-mood
inwisti noun "mind-mood" (changed by Tolkien from inwaldi) (MR:216, 471). The word may seem to be plural in form, despite its singular gloss. Cf. variant inwis above (which could be the singular, if it has the stem inwist-).
inwissar
noun. opal, (lit.) mood-change stone
valwistë
noun. change of mind
walwistë
change of mind
walwistë noun "change of mind" (PE17:189)
walwistë
noun. change of mind
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-.