Thorough, a.
1. Passing through; as, thorough lights in a house. [Obs.]
2. Passing through or to the end; hence, complete; perfect; as, a thorough reformation; thorough work; a thorough translator; a thorough poet.
3 other Webster entries under this spelling
Thorough, prep.
Through. [Obs.] Spenser. Shak.
Thorough, adv.
1. Thoroughly. [Obs. or Colloq.] Chaucer.
2. Through. [Obs.] Shak.
Thorough, n.
A furrow between two ridges, to drain off the surface water. [Prov. Eng.] Halliwell.
Shades of meaning
Fernald has no entry of its own for thorough; he lists it under radical.
Where he writes about it:
The widely divergent senses in which the word radical is used, by which it can be at some time interchanged with any word in the above list, are all formed upon the one primary sense of having to do with or proceeding from the root (L. radix); a radical difference is one that springs from the root, and is thus constitutional, essential, fundamental, organic, original; a radical change is one that does not stop at the surface, but reaches down to the very root, and is entire, thorough, total; since the majority find superficial treatment of any matter the easiest and most comfortable, radical measures, which strike at the root of evil or need, are apt to be looked upon as extreme. — from radical