2. To settle a debt or other financial obligation.
3. To bring in an amount of money: "She wanted to know how much the job would pay."
4. Etymology: from Middle English payen, "to pacify, to appease, to please, to pay"; from Old French paier, from Latin pacare, "to pacify"; from pac-, pax, "peace".
Just as parents, with the objective of having a quiet home, give their babies "pacifiers"; so, employers pay their employees, in an effort to avoid the difficulties of a discontented work force.
Etymologically as well, "to pay" is to pacify. The Latin verb pacare, "to pacify", is derived from pax, "peace". In the Middle Ages, pacare was used specifically to mean "to pacify a creditor by paying a debt" and eventually, more generally "to pay".
The Romance derivatives of the Latin word, including Old French paier, had both the original sense of "to pacify, to please", or "to appease"; and appease like pay and pacify, is a descendant of Latin pax; as well as, the later sense of "to pay".
An additional confirmation of the etymological source of pay
Probably before 1200, paien, "to please, to satisfy, to put money down"; later, "to recompense, to requite, to appease"; borrowed from Old French paiier, from Latin pacare, "to appease, to pacify", or "to satisfy"; especially, a creditor, from pax, "peace".
The meaning in Latin of "to pacify" or "to satisfy" developed through Medieval Latin into that of "pay a creditor", and so "to pay", generally, in the Romance languages (Old French paiier, Provencal, Spanish, Portuguese pagar, Italian pagare, etc.).
In some of these languages, the verb still has both senses; but in French and in English, the sense of "to satisfy" or "to please" has become obsolete.