grimmig
grim
Having a very angry, dark, or relentless facial expression.
Der Trainer schaute seine Mannschaft nach der Niederlage grimmig an.
The coach looked grimly at his team after the defeat.

grim
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grim
Having a very angry, dark, or relentless facial expression.
Der Trainer schaute seine Mannschaft nach der Niederlage grimmig an.
The coach looked grimly at his team after the defeat.

The adjective 'grimmig' is closely related to the noun 'der Grimm', an old term for strong anger or rage. So someone who looks 'grimmig' (grim) shows their anger in their face.
Sein Gesichtsausdruck war voller Grimm.
His facial expression was full of rage.
You can easily recognize the meaning of 'grimmig' from the context. If it refers to a person, their gaze, or their face, it means 'angry' or 'grim'. If it describes the weather or pain, it means 'very intense and unpleasant'.
Der alte König blickte den Boten grimmig an.
The old king looked grimly at the messenger.
When referring to an angry facial expression, 'grimmig' is often combined with verbs of looking or with nouns for the face. Typical phrases are 'grimmig schauen' (to look grim), 'grimmig blicken' (to gaze grimly), or 'eine grimmige Miene' (a grim expression).
Mit grimmiger Miene verließ er den Raum, ohne ein Wort zu sagen.
With a grim expression, he left the room without saying a word.
In the meaning 'intense and unpleasant', 'grimmig' is used almost exclusively for cold or pain. Common combinations are 'grimmige Kälte' (bitter cold), 'grimmiger Frost' (severe frost), or 'grimmiger Schmerz' (severe pain).
Sie zitterte trotz ihrer dicken Jacke in der grimmigen Kälte.
She shivered in the bitter cold despite her thick jacket.
friendly
'freundlich' and 'grimmig' can be opposites when talking about a person’s expression. 'freundlich' describes a kind, open, and pleasant impression. 'grimmig' mainly describes a dark, angry, or hard face. So you are more likely to say that someone smiles in a friendly way or speaks in a friendly way. 'grimmig' is used especially for a look or facial expression when someone seems angry or very stern.

Vor dem Termin schaut Herr Schneider grimmig auf die Rechnung.
Before the appointment, Mr. Schneider looks grimly at the bill.
Der Busfahrer hat den Fahrgästen im Urlaub freundlich geholfen.
The bus driver kindly helped the passengers during the vacation.