ajustar

to adjust, to set; to fine-tune; to fit; to conform to, abide by, act in accordance with; to adjust (oneself/itself)

From justo. Some of the medieval Old Spanish senses (compare Ladino ajustar (“to add”)) seem to correspond better to Vulgar Latin *adiuxtāre or *iuxtāre, from Latin iuxta (compare French ajouter (“to add”)); compare ayustar.