It seems to me that "farcical" includes 2 suffixes, each for the purpose of making an adjective of a noun. I presume this would normally be considered redundant and wrong, but has become dictionary-correct because of common usage.
Do I have that right, or is there some other reason for the word "farcical" being constructed the way that it is?
Farcical is from early 18th century, from farce + suffix -ical.
Suffix -ical has an earlier origin than -ic, with which it is usually Interchangeable. Its usage probably became common because the forms in -ic often took on a noun sense (for example physic).
compound adjectival word-forming element, usually interchangeable with -ic but sometimes with specialized sense (such as historic/historical, politic/political)....... Forms in -ical tend to be attested earlier in English than their twins in -ic.
(Etymonline)
Farcical etymologies are few and far between in the OED, but its etymology of farcical fits.
Etymology: formed as farcic adj. + -al suffix.
This seems to be absurd, because farcical is first attested in 1715, whereas farcic has only one attestation from 1763.
The OED does offer this description of the -ical suffix:.
Many adjectives have a form both in -ic and -ical, and in such cases that in -ical is usually the earlier and that more used. Often also the form in -ic is restricted to the sense ‘of’ or ‘of the nature of’ the subject in question, while that in -ical has wider or more transferred senses, including that of ‘practically connected’ or ‘dealing with’ the subject.
The bold emphasis is mine, because I think this note might be relevant to "farcical." Consider the difference between "comic" and "comical" as an analogy. Something that is "comical" is not necessarily directly related to the art of "comedy."
The comical atmosphere in the room had us all laughing.
Here, "comical" expresses less attachment to "comedy" than would "comic."
Similarly, something that is "farcical" is probably not directly related to the literal meaning of farce:
A dramatic work (usually short) which has for its sole object to excite laughter
