Other forms: suppliants; suppliantly
A suppliant is someone who begs or prays for something, and to be suppliant is to humbly pray or ask for forgiveness. Puppy-dog eyes can help if you’re trying to look suppliant.
Like the related word supplicant, suppliant has do with praying in a humble manner. A suppliant student in the principal's office is going to have better luck avoiding detention than a disrespectful one. Suppliant is not a word you hear much these days — it was more frequently used in the days when people had to beg for everyday things, including basic needs like food and water, from monarchs and others in positions of power or authority.