pro 1 
(pr
ō)
n. pl. pros 1. An argument or consideration in favor of something: weighing the pros and cons.
2. One who supports a proposal or takes the affirmative side in a debate.
adv. In favor; affirmatively: arguing pro and con.
adj. Affirmative; supporting: a pro vote.
[Middle English, from Latin prō, for; see per1 in the Appendix of Indo-European roots.]