IPA: /səˈpoʊzɪdli/
KK: /səˈpoʊzɪdli/
Used to indicate that something is believed to be true or is claimed to be true, but may not actually be the case.
He is supposedly the best player on the team, but I haven't seen him play yet.
Supposedly is formed from "suppose" (from Old French *supposer*, meaning to place under or assume) and "-ly" (a suffix used to form adverbs). The word means in a manner that is assumed or believed to be true.
Think of 'suppose' as placing an idea under consideration, and the '-ly' indicates how something is done. So, supposedly means something is believed to be true in a certain way.