Definition: an old woman
This great noun doesn’t have Latin or Greek origins to it; it is probably a contraction of grandmother! While gammer is dated back to the 1570’s, its male partner, gaffer, also a contraction of grandfather, was first attested 10 years later.
Why this word?
Gammer and gaffer are great synonyms to have when you wish to address the elderly. These words are polite and do not insinuate upon actual age.
How to use the word gammer (or gaffer)?
Simply as a noun synonymous of “old person”.
“The gammer looks absolutely fantastic for her age!”