This is the 3607th most frequent Japanese word.
適切
Appropriate; suitable.
The word '適切' is used to describe the necessity of an appropriate, fitting element (signature).
この書類には適切な署名が必要です。
This document requires an appropriate signature.
Here, '適切' qualifies a solution as suitable and correct for the given context (problem).
問題に適切な解決策を見つけるのは重要です。
Finding an appropriate solution to the problem is important.
In this sentence, '適切' is utilized to describe how certain behavior (comment) fits or does not fit in a social or situational setting.