passend
suitable
To be suitable or appropriate for a particular purpose, situation, or person.
Das war genau die passende Antwort auf seine unverschämte Frage.
That was exactly the suitable answer to his rude question.

suitable / fitting
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suitable
To be suitable or appropriate for a particular purpose, situation, or person.
Das war genau die passende Antwort auf seine unverschämte Frage.
That was exactly the suitable answer to his rude question.

'Passend' (suitable / fitting) is the present participle form of the verb 'passen' (to fit / to suit). When something 'passt' (that is, is suitable or has the right size), then it is 'passend'. This origin helps you understand the meaning.
Ich suche noch ein passendes Geschenk für meine Mutter.
I'm still looking for a suitable gift for my mother.
Whether 'passend' means 'geeignet' (suitable) or 'von der richtigen Größe' (of the right size) can be recognized from context. With abstract things like moments or answers, it means 'suitable'. With concrete things like clothes or keys, it means 'having the right size/shape'.
Das ist der passende Moment, um die Neuigkeit zu verkünden.
This is the suitable moment to announce the news.
In the meaning 'geeignet' (suitable), 'passend' is often combined with the prepositions 'für' (+ accusative) or 'zu' (+ dative). 'Für' describes the purpose, while 'zu' describes the combination with something else.
Dieses Hotel ist passend für Familien mit Kindern.
This hotel is suitable for families with children.
good
'gut' and 'passend' can both express that something is right or useful in a situation. 'gut' is more general and evaluates something positively. 'passend' is more precise: it says that something suits a purpose, a person, a situation, or also fits in size and shape. Learners may confuse the words because, for example, you can say 'eine gute Antwort' (a good answer) and 'eine passende Antwort' (a suitable answer). 'gut' emphasizes quality; 'passend' emphasizes agreement with the situation.

Für das Vorstellungsgespräch sucht Maria eine passende Jacke.
Maria is looking for a suitable jacket for the job interview.
Der Vorschlag des Chefs ist gut, weil er uns viel Zeit spart.
The boss's suggestion is good because it saves us a lot of time.