Confusing Greek Words?

There are some similar Greek words that always seem to cause me a little confusion and embarrassment when I use them in conversation:

Δάχτυλο - δαχτυλίδι (finger - ring) 

λίμνη - λιμάνι (lake - port)

They're probably not confusing at all to others, but I have a minor mental block and a habit of calling a finger a ring. I must learn to repeat, in Greek, "Is that a ring on your finger". Better late than never.