On the find a word site we find 8 meanings of the word FORMAL:
1: n. See Methylal.
2: a. Belonging to the form, shape, frame, external appearance, or organization of a thing.
3: a. Belonging to the constitution of a thing, as distinguished from the matter composing it; having the power of making a thing what it is; constituent; essential; pertaining to or depending on the forms, so called, of the human intellect.
4: a. Done in due form, or with solemnity; according to regular method; not incidental, sudden or irregular; express; as, he gave his formal consent.
5: a. Devoted to, or done in accordance with, forms or rules; punctilious; regular; orderly; methodical; of a prescribed form; exact; prim; stiff; ceremonious; as, a man formal in his dress, his gait, his conversation.
6: a. Having the form or appearance without the substance or essence; external; as, formal duty; formal worship; formal courtesy, etc.
7: a. Dependent in form; conventional.
8: a. Sound; normal.