expression, i-adjective
not having had enough to drink (especially alcohol)
Often used when someone feels they haven't drunk enough alcohol, but can also apply to non-alcoholic beverages. The expression is a negative form of 飲み足りる, which itself is rare.
まだ飲み足りないから、もう一杯頼もう。
I haven't had enough to drink yet, so let's order another round.
水をたくさん飲んだけど、まだ飲み足りない気
I drank a lot of water, but I still feel like I haven't had enough.
Compound of 飲み (continuative form of 飲む 'to drink') + 足りない (negative of 足りる 'to be enough').