Freesia. The flowers come in a great variety of colors - white, golden yellow, orange, red, pink, mauve, lavender and purple. They have a light soapy fragrance.
A filament is a stalk in the flower.
Fantastic or Fashionable can be a compliment starting with letter F.
narrcissus
tulip
nasturtium
Iris
Carnation.
The opposite for the word plain starting with letter f is FANCY.
Finish is another word for completion starting with the letter F.
Orchid (orkid)
halo tree
Dahlia.