IPA: /ʌnˈnoʊtɪsəbl/
KK: /ʌnˈnoʊtɪsəbl/
Something that is not easy to see or detect; it blends in or goes unnoticed.
The changes to the design were so subtle that they were almost unnoticeable.
Unnoticeable → It is formed from "un-" (meaning not) and "notice" (from Latin "notitia", meaning knowledge or awareness) and "-able" (meaning capable of). The word "unnoticeable" means not capable of being noticed or recognized.
Think of 'not' ('un-') being added to 'knowledge' ('notice') to remember that 'unnoticeable' means something that cannot be recognized or seen.