Single word for "inhale using your mouth with force or power"
There are a few words that come to mind, but all have subtle connotations:
- gasp - connotes desperation or exhaustion, the boy gave a gasp of agony.
- gulp - connotes taking in a large quantity of air in a single action, some may gulp air at the water surface but not absorb the contained O2 for respiration.
- suck - connotes drawing in air gradually, he began to suck in air through his mouth.
If I understand what you mean, this is generally described as a sharp intake of breath.
Gasp would be most apt, I reckon.