Is fortuitous a noun or an adjective?

[Lotinmaxceau]

English Grammar Error, Intermediate level

ESL/EFL Test #16 "Sleep well (2)", question 8

This obviously worked because she was very fortuitous and the interview went very well.

(a) obviously
(b) fortuitous
(c) went

English Grammar Error, Intermediate level

ESL/EFL Test #16 "Sleep well (2)", answer 8

This obviously worked because she was very fortunate and the interview went very well.

Correct entry: fortunate
The error was: (b) fortuitous
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is fortuitous a noun or and adjective?

[Torsten]

Any dictionary will tell you that the word 'fortuitous' is an adjective: Definition of fortuitous

TOEIC listening, photographs: A walk in the park