Best definition
The sound a horse makes instead of a neigh, at least according to Spongebob Squarepants.
Found in the episode My Pretty

Seahorse, where Spongebob finds Mystery the seahorse.

Mystery: neighhhhhhh

Mr. Krabs: What was that?

Spongebob: Just practicing my impression of Mystery, Mr. Krabs! Weesnaw!
weesnaw: define #2
Depends on the region of the United States. In the South and Middle America, it is an unmentionable body part. In the West it is a mythical sea horse. In the East, it is an exclamatory remark. It can also be used as a term of affection.
In the South: Uh oh, my weesnaw is really hurting. I better go get this checked out.

In the East: Weesnaw!! The sox won again!

In the West: someday, I hope to catch a Weesnaw.

As a term of affection: I love you my Weesnaw

weesnaw: define #3
What Spongebob Squarepants has said in an episode.
Spongebob : No Mr. Krabs.. that was uhh just me doing my imitation of Mystery. Weesnaw.

Mr. Krabs : Well then.. keep working on it,cause it’s terrible.

(Those probably weren’t the exact words but it’s as close as I can remember.)

weesnaw: define #4
Anything to do with shipping Eridan Ampora from Homestuck.
You say Erifef? I say weesnaw.

via giphy
weesnaw: define #5
Originated from the television show SpongeBob SquarePants, it evolved into garnering a sexual innuendo surrounding the term and eventually became a nickname for the genitals (usually male but can be attributed to female as well) or ejaculation.
“Dude, Victoria was sucking my weesnaw and I couldn’t even get hard”

“Did you even cum?”

“Yeah, I weesnaw’d in her mouth soft!”
weesnaw: define #6
An amazing animal found under the see. Usually pink and yellow. can also be used as a compliment. ” your looking very weesnaw today ”

They are kind and very friendly animals once you get to know one.

“i love you too. ”
weesnaw: define #7
hilary duff
jessie: did you get tickets for weesnaw yet?

josh: yeah and since i preordered, i got a pair of horseshoes, too.