Antonyms of adj informal

4 senses of informal

Sense 1
informal (vs. formal) -- (not formal; "conservative people unaccustomed to informal dress"; "an informal free-and-easy manner"; "an informal gathering of friends")

formal (vs. informal) -- (being in accord with established forms and conventions and requirements (as e.g. of formal dress); "pay one's formal respects"; "formal dress"; "a formal ball"; "the requirement was only formal and often ignored"; "a formal education")
        => ceremonial -- (marked by pomp or ceremony or formality; "a ceremonial occasion"; "ceremonial garb")
        => ceremonious, conventional -- (rigidly formal or bound by convention; "their ceremonious greetings did not seem heartfelt")
        => dress, full-dress -- ((of an occasion) requiring formal clothes; "a dress dinner"; "a full-dress ceremony")
        => form-only (prenominal) -- (being a matter of form only; lacking substance; "a form-only requirement that is usually ignored")
        => full-dress, dress -- (suitable for formal occasions; "formal wear"; "a full-dress uniform"; "dress shoes")
        => nominal, titular -- (existing in name only; "the nominal (or titular) head of his party")
        => positive, prescribed -- (formally laid down or imposed; "positive laws")
        => pro forma, perfunctory -- (as a formality only; "a one-candidate pro forma election")
        => semiformal, semi-formal, black-tie -- (moderately formal; requiring a dinner jacket; "he wore semiformal attire"; "a black-tie dinner")
        => starchy, stiff, buckram -- (rigidly formal; "a starchy manner"; "the letter was stiff and formal"; "his prose has a buckram quality")
        => white-tie -- (requiring white ties and tailcoats for men; "a white-tie occasion")

Sense 2
informal, loose -- (not officially recognized or controlled; "an informal agreement"; "a loose organization of the local farmers")

INDIRECT (VIA unofficial) -> official -- (having official authority or sanction; "official permission"; "an official representative")

Sense 3
informal (vs. formal) -- (used of spoken and written language)

formal (vs. informal) -- ((of spoken and written language) adhering to traditional standards of correctness and without casual, contracted, and colloquial forms; "the paper was written in formal English")
        => literary -- (appropriate to literature rather than everyday speech or writing; "when trying to impress someone she spoke in an affected literary style")

Sense 4
cozy, intimate, informal -- (having or fostering a warm or friendly and informal atmosphere; "had a cozy chat"; "a relaxed informal manner"; "an intimate cocktail lounge"; "the small room was cozy and intimate")

INDIRECT (VIA friendly) -> unfriendly -- (not disposed to friendship or friendliness; "an unfriendly coldness of manner"; "an unfriendly action to take")

Similarity of adj informal

4 senses of informal

Sense 1
informal (vs. formal) -- (not formal; "conservative people unaccustomed to informal dress"; "an informal free-and-easy manner"; "an informal gathering of friends")
       => casual, everyday, daily -- (appropriate for ordinary or routine occasions; "casual clothes"; "everyday clothes")
       => free-and-easy, casual -- (natural and unstudied; "using their Christian names in a casual way"; "lectured in a free-and-easy style")
       => folksy -- (very informal and familiar; "a folksy radio commentator"; "a folksy style")
       => unceremonious, unceremonial -- (without ceremony or formality; "an unceremonious speech")
          Also See-> informal#3

Sense 2
informal, loose -- (not officially recognized or controlled; "an informal agreement"; "a loose organization of the local farmers")
       => unofficial (vs. official) -- (not having official authority or sanction; "a sort of unofficial mayor"; "an unofficial estimate"; "he participated in an unofficial capacity")

Sense 3
informal (vs. formal) -- (used of spoken and written language)
       => colloquial, conversational -- (characteristic of informal spoken language or conversation; "wrote her letters in a colloquial style"; "the broken syntax and casual enunciation of conversational English")
       => common, vernacular, vulgar -- (being or characteristic of or appropriate to everyday language; "common parlance"; "a vernacular term"; "vernacular speakers"; "the vulgar tongue of the masses"; "the technical and vulgar names for an animal species")
       => epistolary, epistolatory -- (written in the form of or carried on by letters or correspondence; "an endless sequence of epistolary love affairs"; "the epistolatory novel")
       => slangy -- (constituting or expressed in slang or given to the use of slang; "a slangy expression"; "slangy speech")
       => subliterary -- (not written as or intended to be literature; "subliterary works such as letters and diaries")
       => unliterary, nonliterary -- (marked by lack of affectation or pedantry; "her talk was very unliterary"- W.D.Howells)
          Also See-> informal#1; unrhetorical#1

Sense 4
cozy, intimate, informal -- (having or fostering a warm or friendly and informal atmosphere; "had a cozy chat"; "a relaxed informal manner"; "an intimate cocktail lounge"; "the small room was cozy and intimate")
       => friendly (vs. unfriendly) -- (characteristic of or befitting a friend; "friendly advice"; "a friendly neighborhood"; "the only friendly person here"; "a friendly host and hostess")