Synonyms for informal

modified

1. Without formality

   casual, natural, relaxed, intimate, unceremonious, unstudied, frank, open, straightforward, free, extempore, spontaneous, congenial, easygoing, easy, unconstrained, unrestrained, unconventional, without ceremony, simple, unpretentious, homey; see also colloquial, friendly 1.

   Antonyms restrained*, ceremonial, ritualistic.

2. Not requiring formal dress

   casual, ordinary, everyday, unofficial, habitual, motley, mixed, democratic, shirt-sleeve, sporty*; see also common 1.

   Antonyms formal, dressy, exclusive.