Final answer:
The plant with a 13-letter name that means 'golden flower' in Greek and is often shortened to just its last three letters is the Helianthus or sunflower.
Step-by-step explanation:
The plant with a 13-letter name that means 'golden flower' in Greek and is often shortened to just its last three letters is the Helianthus or sunflower. The Greek words 'helios' and 'anthos' mean 'sun' and 'flower' respectively. The sunflower gets its name because its bright yellow petals resemble the sun.