Unofficial means not authorised or recognised formally. An unofficial record, unofficial figures, unofficial strike.
It says nothing about accuracy — unofficial figures are often right and simply not yet confirmed — only about who stands behind them. An unofficial strike is one without the union's backing, which changes its legal position entirely. Note that unofficially is often used to introduce the real answer.
1adjectiveunofficialNot authorised or recognised formally.
“He's the unofficial leader of the group, even though nobody ever chose him.”
unofficial is a quality of lacking authority.
Proto-Indo-European
*h₃ep-
Latin
officiālis
Old French
official
Middle English
official
English
official
English, today
unofficial
From un- + official. official comes from Middle English official, from Old French official, from Latin officiālis, from Latin officium (“duty, service”), by surface analysis, office + -ial.
Etymology from Wiktionary, CC BY-SA