In spoken language, people might use "lady" instead of "miss" as a respectful form of address to an unknown (typically older) woman: e.g. "excuse me, lady, do you know what time it is?" instead of "excuse me, miss, ..."
However, both of these usages are old-fashioned and might be considered mildly offensive (especially when used as a form of address). Using it indirectly as a synonym for "woman" ("I saw a lady cross the street") is still old-fashioned, but less potentially problematic. In my ear it also sounds class-laden - the way a working class male (taxi driver, construction worker, etc.) would speak to an (unknown) upper class woman.
"Ma'am" (short for "madam", the female equivalent of "sir") would be less old-fashioned, although still a bit awkward - this also avoids the difficulty of categorizing the unknown person as young/unmarried ("miss") vs older ("lady"). To be honest, if I have to address an unknown woman I would probably avoid the problem entirely and address her directly. ("Excuse me, do you know what time it is?")