IPA: /ˌʌn.əbˈtruː.sɪv.nəs/
KK: /ʌnəbˈtruːsɪvnəs/
The quality of not attracting attention or being noticeable; being discreet and subtle.
Her unobtrusiveness made her a perfect guest at the party, as she blended in without drawing any attention.
Unobtrusiveness → It is formed from "un-" (meaning not), "obtrusive" (from Latin "obtrudere", meaning to thrust forward), and "-ness" (meaning the state of being). The word describes the state of not being thrust forward or noticeable, hence being discreet or inconspicuous.
Think of 'not' ('un-') being 'thrust forward' ('obtrusive') — unobtrusiveness means being in a state of not drawing attention.