Taken as a type of something green; the word may also mean the season when the grass grows, spring and early summer.
In literary or poetic use, grass is often referred to as growing over and covering graves and battlefields. The image may also cover the idea of grass growing in the streets of a formerly prosperous community returning to the wilderness.
The word is recorded in Old English (in form græs) and is of Germanic origin, ultimately related to green and grow.
the grass is always greener on the other side of the fence mid 20th century, meaning that something just out of reach always appears more desirable than what one already has. The idea is an old one; the Roman poet Ovid in Ars Amatoria has, ‘the harvest is always more fruitful in another man's fields.’
grass roots the most basic level of an activity or organization, a figurative use recorded from the early 20th century, and now particularly applied in politics to the rank-and-file of a political organization.
grass widow a woman whose husband is away often or for a prolonged period. In the early 16th century, the word denoted an unmarried woman with a child, perhaps from the idea of the couple having lain on the grass instead of in bed. The current sense dates from the mid 19th century.
not let the grass grow under one's feet not delay in acting or taking an opportunity.
put out to grass force to retire, make redundant. Used literally of putting a horse or other animal out to graze. In figurative use since the late 16th century, the earlier form of the expression was with turn (out) rather than put out.
while the grass grows, the steed starves dreams or expectations may be realized too late; proverbial saying, mid 14th century.
See also snake in the grass.