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a really large or sizeable object. The main focus being put on wild animals, however, It could relate to any object that causes a reflex dropping of jaw.
Whitetail deer, tom turkeys, rainbow or brown trout.

My God, that deer is a thooster!! Look at the size of its rack!!
by sevobuck September 14, 2010
noun; a reference to anything that is bigger than the usual size
"That cigar is a thooster!"
by Bidgit July 24, 2009