massig
plenty
Colloquial for a very large amount or number of something.
Auf der Party gab es massig zu essen und zu trinken.
There was plenty to eat and drink at the party.

plenty / massive
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plenty
Colloquial for a very large amount or number of something.
Auf der Party gab es massig zu essen und zu trinken.
There was plenty to eat and drink at the party.

The adjective 'massig' (plenty/massive) is derived from the noun 'die Masse' (mass). This explains both meanings: a large 'Masse' (mass) of something, as in 'Massen von Menschen' (masses of people), or an object that has a lot of physical 'Masse' (mass) and is therefore heavy.
Im Lager standen massige Kisten aus Eichenholz.
Massive crates made of oak stood in the warehouse.
When 'massig' (plenty) describes a large amount, it often stands alone or is used with things like 'Zeit' (time), 'Geld' (money), or 'Leute' (people). When it describes an object as heavy and compact, it usually appears as an adjective directly before a noun like 'Schrank' (cabinet) or 'Stein' (stone).
Ich habe massig Fehler im Text gefunden.
I found plenty of mistakes in the text.
In the meaning 'sehr viel' (a lot), 'massig' (plenty) is a typical colloquial word. It is used less often in more formal or written contexts.
Wir haben noch massig Zeit, bis der Zug fährt.
We still have plenty of time before the train leaves.
In the colloquial meaning 'sehr viel' (a lot), 'massig' (plenty) can be used like an adverb or an undeclined adjective. It then remains unchanged before a noun.
Auf dem Festival waren massig Leute.
There were plenty of people at the festival.
In the meaning 'schwer und kompakt' (heavy and compact), 'massig' (massive) is often used to describe sturdy furniture, structural components, or strongly built people or animals.
Sein massiger Körper passte kaum auf den kleinen Stuhl.
His massive body barely fit on the small chair.
much / a lot
'viel' and 'massig' can both express a large amount. 'viel' is neutral and fits almost any situation, including formal texts. 'massig' is colloquial and feels stronger. It does not just mean 'a lot', but more like 'a great deal' or 'more than enough'. That is why 'massig' sounds especially natural in casual conversations, for example about work, food, problems, or people. If the sentence should sound factual or polite, 'viel' is usually more appropriate.

Im Büro gibt es heute massig zu tun.
There is tons to do at the office today.
Heute habe ich viel Arbeit und kann erst später kommen.
I have a lot of work today and can only come later.