Mighty, a. [Compar. Mightier; superl. Mightiest.]
Etymology: [AS. meahtig, mihtig; akin to G. mächtig, Goth. mahteigs. See Might, n.]
1. Possessing might; having great power or authority. Wise in heart, and mighty in strength. Job ix. 4.
2. Accomplished by might; hence, extraordinary; wonderful. "His mighty works." Matt. xi. 20.
3. Denoting and extraordinary degree or quality in respect of size, character, importance, consequences, etc. "A mighty famine." Luke xv. 14. "Giants of mighty bone." Milton. Mighty was their fuss about little matters. Hawthorne.
2 other Webster entries under this spelling
Mighty, n.; pl. Mighties.
A warrior of great force and courage. [R. & Obs.] 1 Chron. xi. 12.
Mighty, adv.
In a great degree; very. [Colloq.] "He was mighty methodical." Jeffrey. We have a mighty pleasant garden. Doddridge.
Shades of meaning
Fernald lists mighty only as an antonym, under pitiful.
He lists it without comment; the entries above explain its neighbors.