IPA: /ˌɒpəˈtjuːnəs/
KK: /ˌɑːpərˈtunəs/
The quality of being suitable or advantageous at a particular time.
The opportuneness of her arrival allowed us to discuss the project before the meeting.
Opportuneness is formed from "opportunus" (from Latin, meaning favorable or suitable) and the suffix "-ness" (meaning the state or quality of). The word refers to the quality of being favorable or suitable for a particular purpose or situation.
Think of 'favorable' ('opportunus') to remember that 'opportuneness' means the quality of being suitable or advantageous.