IPA: /ˌʌn.dɪsˈɒlvd/
KK: /ʌnˈdɪsˌɔlvd/
Not mixed into a liquid; remaining in solid form.
The undissolved particles settled at the bottom of the container.
Undissolved → It is formed from "un-" (meaning not) and "dissolved" (from Latin "dissolvere", meaning to loosen or dissolve). The word "undissolved" means not having been loosened or dissolved, indicating that something remains intact or whole.
Think of 'not' ('un-') having been 'loosened' or 'dissolved' — that's why undissolved means something that hasn't broken down.