A while ago, one of Something Awful's pretending-to-be-horrified-but-actually-acting-as-direct-product-placement-for-J-list porn reviews (hey, everyone's got to make a living) demonstrated the power of context-based language learning when its author successfully deduced that zenra meant "naked".

In kanji, you write it like this: 全裸, literally "completely naked". This is a Sino-Japanese word, though: there are a surprising number of native Japanese synonyms. In fact, they act as a pretty good catalogue of the common prefixes meaning "completely".

• akahadaka (赤裸), "red-naked". The most convincing theory I've heard for why "red" = "completely" is that aka is related to words like akarui, which means "bright", and therefore "obvious" -> "unmistakably, completely". (I guess it might also be related to the aka in words like akachan for "baby", since babies are born naked and all -- but since there are also words and phrases like akahage ("red [= completely] bald") and aka no tanin ("a red [= complete] stranger"), I prefer the more general explanation.)
• maruhadaka (丸裸), "round-naked". This one is so much easier. Something which is round has no discontinuities or awkwardness in its outline, therefore it is whole and/or complete. You can put maru before periods of time to emphasise their fullness (think "one week" vs "a solid week"), and it's also the meat of the very common phrase maru de ("just like..." or "completely").
• hitahadaka (直裸), "just naked". This one must be pretty rare, because I hadn't heard of it before I started writing this post, and the Windows kanji entry system doesn't know it either. Apparently the hita here is probably related to hito, the old, old, ooold Japanese lexeme for "one". It's the same hita as in the fairly common word hitasura, which can mean a variety of things related to singleness and completeness. ("Merely", "single-mindedly", "completely", etc.)
• mappadaka (真っ裸), "truly naked". Another easy one. Note that the ha at the start of hadaka has turned into a ppa.
• suppadaka (素っ裸), "fundamentally naked" or maybe "purely naked". This one doesn't really belong here because the su is Chinese. I'm letting it in out of sympathy, though, because little 素 here doesn't even have a proper Japanese reading. The only native Japanese work it can get is obvious subbing for other kanji in words like 素人 (shirouto, etymologically "white person" (白人) but meaning "amateur") and 素より (motoyori, "from the beginning" (元より)). This, plus the fact that su causes the exact same ppa-ing as ma, has led me to grant su official status as a lexeme so thoroughly assimilated into Japanese that it might as well be native. You can also see it in the word suppin, which is probably from 素品, "fundamental/unblemished appearance/character", and means "face without make-up".

Anyone know any others?