A Google Web Search Help thread has a case where the Google Dictionary showed a picture of a topless woman for the definition of [perverse].
I was able to replicate the naked woman for that term this morning, so it may still show up for you.

Sarah, a Google User Experience Specialist, explained the issue:
There are a couple of things going on here that could explain why the image made it through Safe Search. Thomas P made some really great points. Just for future knowledge, when issues like this occur help us out and click the Safe Search link next to the Search box and then click to report offensive image. Click the report button on that image and voila!I took care of reporting this one for you so you don't need to worry about it, but good knowledge any future occurrences.
This may be the first report of nudity in Google's Dictionary.
Forum discussion at Google Web Search Help.

Comments:
Black Seo Guy
07/28/2011 01:14 pm
Sometime a hippo can out run a lion..yea I know this sound crazy but I'm trying to say that sometimes things happen. "Black Seo Guy "Signing Off"
seogabs
07/28/2011 01:58 pm
she has gone now, bye bye lady ;)
Michael Roberts
07/28/2011 02:15 pm
Still showing for me... kinda funny to be honest.
Michael Roberts
07/28/2011 02:15 pm
[oops... double posted somehow]
Horny
07/29/2011 09:38 am
Why did you people reported it? Its gone for good now :(
Nasif
08/03/2011 11:01 pm
lolz
Robin_salmansohn
08/07/2011 08:46 am
Was Google hacked? Did this incident take Google dictionary down forever? You can use define:perverse.
Lizncoetzee
11/03/2011 01:07 am
Looking up a word in my classroom with a class of Junior High School Boys, this porn video was thrown on the big screen unintentionally. I think it's sad that people are even allowed to post videos like this. I tried to remove by following advice on the Youtube site, but find no flag where I can click to remove 'sexual content'. The only thing I could find is a box with the URL here below. I feel assaulted by this content. Could you please help to remove? EJZ Coetzee