In-fôrm'al, a.

a. [Prefix in, not, and formal; Sp. in-formal.]

1. Not in the regular, usual, or established form; without official, conventional, or customary forms; hence, without ceremony; as, an informal writing, proceeding, or visit.
2. Irregular or deranged in mind. [Obs.] “These poor informal women.” Shak.