meinen
to think
To have and express a particular opinion or view. It is often used to express a personal belief.
Ich meine, wir sollten das Angebot annehmen.
I think we should accept the offer.

to think / mean
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to think
To have and express a particular opinion or view. It is often used to express a personal belief.
Ich meine, wir sollten das Angebot annehmen.
I think we should accept the offer.

Although 'meinen' sometimes means 'to mean', its most common meaning is 'to think' or 'to have an opinion'. When someone begins a sentence with 'Ich meine, ...' (I think/mean ...), they are expressing their personal view.
Ich meine, das ist eine gute Idee.
I think that is a good idea.
To express an opinion, 'meinen' (to think) is very often used with a subordinate clause introduced by 'dass' (that). The conjugated verb of the subordinate clause then comes at the end.
Der Experte meint, dass die Preise weiter steigen werden.
The expert thinks that prices will continue to rise.
In the meaning of 'sich beziehen auf' (to refer to), 'meinen' (to mean) is often used in questions to avoid misunderstandings. Typical questions are 'Wen meinst du?' (Who do you mean?) or 'Was meinst du damit?' (What do you mean by that?).
Meinst du den neuen Kollegen aus der Buchhaltung?
Do you mean the new colleague from accounting?
To emphasize the seriousness of a statement, 'meinen' (to mean) is often combined with adverbs such as 'ernst' (seriously), 'ehrlich' (honestly), or 'wörtlich' (literally).
Glaub mir, ich meine das absolut ehrlich.
Believe me, I mean that absolutely honestly.
The idiom 'es gut mit jemandem meinen' (to mean well by someone) is a fixed structure. The person the good intentions are directed toward is always in the dative.
Deine Eltern meinen es nur gut mit dir.
Your parents only mean well by you.
to know
'wissen' and 'meinen' can both appear in sentences about statements or thoughts. 'wissen' is used when you know a fact for certain. 'meinen' is used when you express an opinion or want to explain what you are referring to. The words can easily be confused because you are often talking about the same topic, but with different levels of certainty. 'Ich weiß, dass der Zug um acht fährt' (I know that the train leaves at eight) sounds certain. 'Ich meine, der Zug fährt um acht' (I think the train leaves at eight) sounds more like a guess or personal view.

Yara meint, dass der neue Drucker für das Büro zu teuer ist.
Yara thinks that the new printer is too expensive for the office.
Nach dem Gespräch wusste der Mitarbeiter, wann die Familie ankommt.
After the conversation, the employee knew when the family would arrive.