expression, ichidan verb
add meat; add weight; add substance
Literally 'to attach meat', used both for adding actual meat to a dish and figuratively for adding substance, detail, or weight to something like an essay or argument.
スープにもっと肉を付けてください。
Please add more meat to the soup.
このレポートはまだ薄いので、もう少し肉を付けないといけない。
This report is still thin, so I need to add more substance to it.