1. superlative form of posy; most resembling or characteristic of a posy (a small bouquet of flowers)
Usage: rare; primarily used in descriptive or literary contexts
2. superlative form of posy; most affected, pretentious, or excessively dainty in manner or appearance
Usage: informal; chiefly British

Examples

• The posiest arrangement in the shop featured delicate roses and baby's breath.
• Her posiest mannerisms made her seem out of place at the casual gathering.
• The garden's posiest corner was filled with fragrant wildflowers.
• He found her posiest affectations rather tiresome.
• The posiest decoration on the table was a small vase of violets.