
stöhnen
to groan / moan
To make a deep, inarticulate sound that expresses pain, great effort, or also pleasure.
Der Patient stöhnte leise vor Schmerz.
The patient groaned softly in pain.
to groan / moan
Loading your saved state.

to groan / moan
To make a deep, inarticulate sound that expresses pain, great effort, or also pleasure.
Der Patient stöhnte leise vor Schmerz.
The patient groaned softly in pain.

to complain about
To complain loudly and plaintively about a burden or a difficult situation.
Die Mitarbeiter stöhnen über die hohe Arbeitsbelastung vor den Feiertagen.
The employees are complaining about the heavy workload before the holidays.
The two meanings can be distinguished well by the grammar. When someone complains about something, the preposition 'über' (+ accusative) is always used. When someone makes a sound because of pain or effort, the verb often stands alone or with 'vor' (+ dative).
Er stöhnte vor Schmerz, als der Arzt das Bein untersuchte.
He groaned in pain when the doctor examined his leg.
To express the cause of the physical groaning, you use the preposition 'vor' followed by the dative. Typical causes are pain, effort, or pleasure.
Der Läufer stöhnte vor Anstrengung, als er den Berg hinauflief.
The runner groaned with effort as he ran up the mountain.
When 'stöhnen' is used in the sense of 'sich beschweren' (to complain), it always takes the preposition 'über' with the accusative. This names the topic of the complaint.
Im Sommer stöhnen alle über die unerträgliche Hitze in der Stadt.
In summer, everyone complains about the unbearable heat in the city.
The use of 'stöhnen über' (to complain about) is rather colloquial and very vivid. It expresses that someone is complaining very intensely and audibly.
Mein Kollege stöhnt schon wieder über seine lange To-do-Liste.
My colleague is already complaining again about his long to-do list.
to complain / sue / lament
Klagen can express a matter-of-fact or calm complaint about a burden. By contrast, stöhnen über a burden sounds loud and emotional, making the effort or suffering clearly audible. Klagen fits a neutral statement, while stöhnen describes an audible reaction to strain.

Nach der langen Schicht stöhnte Lea laut über ihre Rückenschmerzen.
After the long shift, Lea groaned loudly about her back pain.
Nach der langen Schicht klagte Lea ruhig über ihre Rückenschmerzen.
After the long shift, Lea calmly complained about her back pain.