Beheaded, a musical instrument;
Beheaded and transposed, I denote equality.
Answer: Sharp, harp, par.
Complete, I'm in a difficulty.
Behead me, and I show signs of grief.
Once more, and I am a useful seed;
Again, and I am what philosophers name our ancestors.
Transposed, I am a vegetable.
Answer: Scrape, crape, rape, ape, pea.
Complete, I am a reproof.